Synthesis of Racemic and Enantiomerically Pure (R*,R*,R* )-Tris(α-methylbenzyl)phosphane - X-ray Crystal Structures of the Phosphane Oxides and Borane Complexes

Article abstract of DOI:10.1002/ejoc.200300396

An asymmetric synthesis of C₃-symmetric phosphane 1 has been achieved. Two of the α-methylbenzyl groups were introduced as nucleophiles (using an α-methylbenzyl Grignard reagent), and asymmetry was introduced by resolution using (R)-α-methylbenzylamine. The final α-methylbenzyl group was introduced as an electrophile (α-methylbenzyl iodide) in a modestly selective reaction. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200300396

FULL PAPER
Synthesis of Racemic and Enantiomerically Pure (R*,R*,R*)-Tris(α-
methylbenzyl)phosphane ؊ X-ray Crystal Structures of the Phosphane Oxides
and Borane Complexes
Paul Wyatt,*[a] Helen Eley,[a] Jonathan Charmant,[b] Berian J. Daniel,[b] and
Anob Kantacha[b]
Keywords: Phosphanes / Asymmetric synthesis / C3 symmetry / Boranes
An asymmetric synthesis of C3-symmetric phosphane 1 has
been achieved. Two of the α-methylbenzyl groups were in-
troduced as nucleophiles (using an α-methylbenzyl Grignard
reagent), and asymmetry was introduced by resolution using
(R)-α-methylbenzylamine. The final α-methylbenzyl group
was introduced as an electrophile (α-methylbenzyl iodide) in
a modestly selective reaction.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
Monodentate phosphorus ligands are back in vogue.[1Ϫ3]
Enantiomerically pure C3-symmetrical phosphanes 2 are
known,[4,5] and while transition metal complexes with con-
gested phosphane ligands like tBu3P and Cy3P have been
shown to have unusual catalytic properties,[6,7] those of
enantiomerically pure C3-symmetrical phosphanes 3 have
shown promise in asymmetric reactions.[8,9] We report here
the asymmetric synthesis of a phosphane 1 that is mono-
dentate, C3 symmetrical and where the chiral centres are
as close to phosphorus as possible while avoiding a chiral
phosphorus atom itself. We report the X-ray crystal struc-
ture of the oxide and borane complex.
yield (Scheme 1). The standard difficulties with benzyl
Grignard preparation were largely overcome using the
method from Brown et al., which involves the mechanical
grinding of the magnesium turnings for five days.[10] Al-
though statistics are against us — a purely statistical out-
come from this reaction would yield a 3:1 ratio of C1:C3
phosphanes — the ratio of diastereomers was 1:1. There-
fore, a 1:1 mixture of diastereomers, though a little unusual,
actually represents a stereoselective reaction. The desired
diastereomer was isolated by recrystallisation. As we have
found before,[11] C3-symmetrical compounds have a greater
tendency to crystallise than their less symmetrical dia-
stereomers. This was useful for purification purposes for all
of the C3-symmetrical compounds described in this paper.
Results and Discussion
Synthesis of Racemic Phosphane Oxide and Borane
The synthesis of the racemic phosphane oxide 4 was
reasonably straightforward; α-methylbenzyl Grignard re-
agent was reacted with PCl3 followed by H2O2 to give a
mixture of the diastereomeric phosphanes 4 and 5 in 59%
[a]
School of Chemistry, University of Bristol,
Cantock’s Close, Bristol, BS8 1TS, England
Fax: (internat.) ϩ44-(0)117-929-8611
E-mail: paul.wyatt@bristol.ac.uk
[b]
Structural Chemistry Laboratory, University of Bristol,
Cantock’s Close, Bristol, BS8 1TS, England
Fax: (internat.) ϩ44-(0)117-929-050
As is common with phosphane chemistry, our plan was
to isolate the corresponding phosphane oxide 4 of the phos-
phane 1 and our initial plan for an asymmetric route fea-
E-mail: jon.charmant@bristol.ac.uk
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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Racemic and Enantiomerically Pure (R*,R*,R*)-Tris(α-methylbenzyl)phosphane
FULL PAPER
thwarted when it came to liberating the phosphane due to
the reduction difficulties discussed above. Attempted reso-
lution of the phosphane using the asymmetric borane
IpcBH2 was also not successful.[19] Any complexes that were
formed were too unstable to be useful. Resolution of the
completed phosphane was abandoned and alternative
asymmetric syntheses were investigated.
Asymmetric Synthesis using Electrophilic Phosphorus
A key intermediate in the strategy for asymmetric syn-
thesis was phosphinic acid 13, which contains two of the
three α-methylbenzyl groups with the correct relative and
absolute stereochemistry. Introduction of the final α-meth-
ylbenzyl unit to some derivative of this acid (12 or 14) was
to be done exploiting the electrophilic properties of phos-
phorus.
Scheme 1. Preparation of racemic phosphane oxide 4
tured phosphane oxide 4 as an intermediate. However, we
were unable to reduce the phosphane oxide to its phos-
phane. The usual conditions of AlH3,[12] HSiCl3 [13] and Li-
AlH4 [14,15] (at room temperature) failed to reduce the oxide
4. The phosphane oxide responded to more persuasive
methods (LiAlH4 in refluxing THF) with a debenzylation
to give the phosphinous acid 6 (Scheme 2).
Following a procedure outlined by Denmark et al.[20] we
reacted PCl3 with α-methylbenzyl Grignard reagent fol-
lowed by (R)-α-methylbenzylamine and finally H2O2 to give
all four diastereomers of the phosphinic amide products
8Ϫ11 (Scheme 3). Two of these diastereomers 10 and 11
contain a stereogenic phosphorus atom while the other two
contain a non-stereogenic phosphorus atom (stereochem-
istry is indicated in Figure 1; the phosphorus atom is, in
essence, a pseudoasymmetric centre. Pseudoasymmetric
centres are more commonly encountered when they are
Scheme 2. Attempts to form 1 and its reaction products
Clearly the phosphane oxide could not feature as an in-
termediate in our asymmetric route and we therefore sought
an alternative. Reaction of PCl3 with α-methylbenzyl Grig-
nard reagent followed by BH3·THF (instead of H2O2) gave
the phosphaneϪborane complex 7 (and its diastereomer) in
a combined yield of 52%. As would be expected, the dia-
stereomeric ratio was similar to the oxide with a ratio of
1:1. Removal of the borane to reveal the phosphane was
easily achieved using Et2NH in 90% yield (Scheme 2).[16,17]
We then tested the sensitivity of the phosphane 1 in air.
Although we had considered its oxidation to oxide 4 in air,
we had not expected the alternative debenzylation reaction
to the phosphinous acid 6. It is interesting to note that de-
benzylation happens under both oxidative (air) and re-
ductive (with LiAlH4) conditions (Scheme 2).
Scheme 3. Preparation of four phosphinic amides and the sub-
sequent reaction of 9; reagents a) i) PCl3; ii) (R)-α-methylbenzyl-
amine; iii) H2O2; b) Separation, c) HCl/dioxane reflux
Attempted Resolution
Phosphane oxides can be resolved by a variety of tech-
niques.[18] Most straightforward are those employing acids.
We were not successful in any attempt to resolve the phos-
phane oxide using camphorsulfonic acid or tartrate deriva-
tives. But in any case, success here would have been Figure 1. Stereochemistry
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P. Wyatt, H. Eley, J. Charmant, B. J. Daniel, A. Kantacha
FULL PAPER
stereogenic and achirotopic.[21] Clearly the phosphorus
atom is not included by these conditions as it is chirotopic
by virtue of the α-methylbenzyl group of the phosphinam-
ide. However, there is no link between its stereoisomerism
and chirality (it is not a chiral centre as it has two enanti-
otopic α-methylbenzyl groups attached).[22] The descriptors
necessary (s and r) are also characteristic of a standard
pseudoasymmetric centre).[21,22] The diastereomer 9 was the
second most abundant from this procedure. Hydrolysis gave
the phosphinic acid 13, which was readily converted into
the phosphinic acid chloride 12 or ester 14. However, reac-
tion of 12 or 14 with α-methylbenzyl Grignard reagent
failed. It was at this point that we also learned from our
investigation into the racemic material that we were unable
to reduce the phosphane oxide 4 anyway. Hence any asym-
metric route (or, indeed, any route to racemic materials)
would have to exclude the oxide 4 as an intermediate.
Scheme 5. Model experiments; preparation and alkylation of
diphenylphosphaneϪborane; reagents: a) (i) LiAlH4, (ii) BH3·
THF; b) (i) KOH/MeOH, (ii) MeI; c) (i) nBuLi, (ii) PhCHIMe
The methylation of the borane complex 17 with KOH
and MeI is known[23] and was repeated without difficulty,
but the reaction with KOH and α-methylbenzyl chloride did
not lead to alkylation. After some investigation we deter-
mined that successful alkylation (51% yield) could be
achieved to give 18 using nBuLi as the base and α-meth-
ylbenzyl iodide[24] as the electrophile.
Scheme 4. A strategy based on the nucleophilic phosphorus
Asymmetric Synthesis Using Nucleophilic Phosphorus
Faced with the difficulties of using an electrophilic phos-
phorus atom, we decided to change to a strategy using a
nucleophilic phosphorus atom. Because we had established
that boron could be removed from 7, the successful forma-
tion of a nucleophilic species 16, followed by alkylation
would represent a route to the free phosphane 1. Thus
either bis(α-methylbenzyl)phosphane itself or its boron
Scheme
6.
Preparation
and
alkylation
of
bis(α-
methylbenzyl)phosphaneϪborane; reagents: a) SOCl2; b) (i) Li-
AlH4, (ii) BH3·THF; c) (i) nBuLi, (ii) α-methylbenzyl iodide, iii)
separation; d) Et2NH
These conditions were applied to phosphinic chloride 12
complex 15, would be prepared and then alkylated. The to give complex 15 in 60% yield and the alkylated product 7
method for the introduction of two of the three absolute in 55% yield in a 2:1 ratio in favour of the C3 diastereomer.
stereocentres was the same and so phosphinic acid 13 was Curiously, reaction of 15 with KOH/MeOH and MeI fails.
again a key intermediate.
Separation and purification of the single diastereomer low-
A method for the conversion of acid 13 to complex 15 ered the yield to 22%. The ratio of diastereomers to be ex-
was needed as was a method for the alkylation of 15. Model pected statistically is 1:1. Initially, we used just over one
experiments were conducted with diphenylphosphinic acid equivalent of alkyl iodide but, since it is racemic, this would
to find suitable conditions (Scheme 5). The reduction of necessarily limit the ratio of products to 1:1. To at least
Ph2PCl to its phosphaneϪborane Ph2PH·BH3 has been re- allow the possibility of kinetic resolution (where the lithium
ported using a combination of LiAlH4 and BH3·THF.[17] phosphide can choose to react with the enantiomer it
We found that the efficacy of this reagent combination ex- wishes) we used five equivalents of alkyl iodide. Thus the
tended to Ph2POCl for the formation of complex 17 (54% small improvement in selectivity to 2:1 was noted. The final
yield; Scheme 5). It would have been more convenient to step in the asymmetric synthesis was removal of borane
reduce acid 13 directly but conditions effective for reduction using Et2NH. This reaction had been established in the ra-
of Ph2POH (i.e. LiAlH4/NaBH4/CeCl3) are low yielding for cemic sequence and proceeded as expected to give phos-
phosphinic acids.[17]
phane 1 in 90% yield.
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Racemic and Enantiomerically Pure (R*,R*,R*)-Tris(α-methylbenzyl)phosphane
FULL PAPER
Optically Pure Phosphane-Borane 7
X-ray crystal structure determination was performed on
the phosphaneϪborane complex 7 (Figure 2).
Figure 4. ORTEP drawing of phosphane oxide 4
plexes but the α-methylbenzyl groups twist slightly further
so that the methyl groups are closer to the PϭO bond. Thus
the dihedral angle between the PϭO bond and the benzylic
CϪH bond varies between 152.0° and 154.8°. The CϪP
˚
bond lengths are 1.8469(19), 1.848(2) and 1.851(2) A.
Figure 2. ORTEP drawing of the phosphaneϪborane 7
NMR Spectra
The visually apparent symmetry in the crystal structure
is not crystallographic and thus not reflected in the space
group. The CϪP bond lengths are 1.864(7), 1.847(7) and
It is instructive to compare the expansions of NMR spec-
tra of the C3-symmetrical phosphane and its diastereomer
with the spectra of the C3-symmetrical amine 20 and its
diastereomer 21.[11] The expansions (δ ϭ 3.5Ϫ0.5 ppm for
phosphanes and δ ϭ 5.0Ϫ0.5 ppm for amines) in the fol-
lowing figures include signals from the benzylic protons and
methyl protons. The C3-symmetrical diastereomer of
phosphaneϪborane 7 contains an unremarkable double
doublet corresponding to the three homotopic methyl
groups (Figure 5). The other diastereomer 19 contains three
diastereotopic methyl groups which are immediately evident
˚
1.858(7) A while the CϪPϪC bond angles are 105.0(3)°,
105.0(3)° and 102.8(3)°. Most interesting is the cone angle
for the phosphane which is estimated from this crystal
structure to be 183.4°. This large cone angle is similar to
the 182° of tBu3P[25] and a view from the side (Figure 3)
shows how well the phosphorus atom is embedded in the
structure. A good way to consider the orientation of the
α-methylbenzyl groups in the structure is to note that the
carbonϪbenzylic proton bond approaches antiperiplanarity
with the PϪB bond (the dihedral angles are between 165.7°
and 170.4°). This is in stark contrast to the orientation of
the benzyl groups in the analogous amine 20.[11]
1
in the H NMR spectrum (Figure 6).
Figure 3. Side view of phosphaneϪborane 7
1
Figure 5. H NMR spectrum of phosphaneϪborane 7
Racemic Phosphane-Borane (؎)-7 and
Phosphane Oxide (؎)-4
The crystal system of the racemic borane complex is
The C3-symmetric diastereomer of amine 20 (Figure 7)
monoclinic with a P21/c space group.
contains a doublet for the three homotopic methyl groups.
The appearance of the crystal structure is visually very But this time in the other diastereomer there are only two
similar to the optically pure borane. The crystal system of diastereotopic methyl groups present in a 2:1 ratio. Once
1
¯
the racemic phosphane oxide is triclinic with a P1 space again this is revealed in the H NMR spectrum (Figure 8).
group. Again it is very similar to that of the borane com- The difference between the diastereotopic characteristics of
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P. Wyatt, H. Eley, J. Charmant, B. J. Daniel, A. Kantacha
FULL PAPER
Conclusion
The asymmetric synthesis of the interesting molecule 1
has proved challenging and the overall yield from α-meth-
ylbenzyl alcohol is approximately 1%. The asymmetric part
of the synthesis depends upon (R)-α-methylbenzylamine as
a resolving agent and the three α-methylbenzyl groups
themselves are introduced by both nucleophilic and electro-
philic methods. Although the free phosphane itself is very
air sensitive and resisted our attempts to characterise it
thoroughly, the formation of a metal complex can be
achieved in situ once the phosphane is liberated from its
borane complex. The NMR spectra of rhodium complexes
with the phosphanes are included in the Supporting Infor-
mation (see also footnote on the first page of this article).
The application of these complexes is being investigated.
1
Figure 6. H NMR spectrum of phosphaneϪborane 19
Experimental Section
General Experimental Details: All reactions, unless otherwise
stated, were performed under nitrogen in glassware that had been
dried overnight in an oven at 150 °C. Reactions were monitored by
TLC using glass-backed silica gel F254 plates (Merck) and visual-
ised using UV254nm or by iodine adsorption as appropriate. Flash
column chromatography[28] was carried out routinely using 60-A
˚
silica gel (Fluorochem). Reagents were used without further purifi-
cation from commercial sources unless otherwise stated. Petroleum
ether refers to the fraction with 40Ϫ60 °C boiling point range.
NMR spectra were recorded with a Joel Delta/GX 270, 400, a
Lambda 300 or an Eclipse 300 MHz spectrometer. Mass spectra
were recorded with a VG analytical autospec mass spectrometer. IR
spectra were recorded with a PerkinϪElmer 881 IR spectrometer in
the solid state or as a liquid film. [α]D Values were recorded with
a PerkinϪElmer 241 MC polarimeter and are given in 10Ϫ1
1
Figure 7. H NMR spectrum of amine 20
deg·cm2·gϪ1
.
Anhydrous solvents were obtained by passing HPLC grade solvents
through a modified Grubbs system[29] manufactured by anhydrous
engineering. De-oxygenated solvents were prepared by passing a
stream of N2 through the solvent of choice at room temperature
via a fine capillary for 2 h prior to use.
HPLC measurements were made using Gilson 712 HPLC system
controller software, a dynamic absorbance detector (model UV 1),
dynamic mixer 811C, manomeric module 806, a Gilson 506C sys-
tem interface module and Gilson pumps 305 and 303.
Preparation of Racemic Materials
(؎)-1-Chloro-1-phenylethane: sec-Phenethyl alcohol (20.0 mL,
166 mmol) was dissolved in CHCl3 (100 mL) in a dry three-necked
round-bottomed flask and the solution stirred at room tempera-
ture. A solution of thionyl chloride (11.0 mL, 151 mmol) in CHCl3
(30 mL) was added dropwise to the mixture over 2 h. The sulfur
dioxide evolved was quenched by bubbling through a saturated
NaHCO3 solution. The mixture was then stirred overnight at room
temperature. Saturated aqueous NaHCO3 solution (150 mL) was
added to the reaction mixture and the aqueous layer was extracted
with CHCl3 (3 ϫ 100 mL). The organic phases were combined,
dried (MgSO4) and concentrated under reduced pressure yielding
a crude yellow oil which was purified by distillation under reduced
pressure to give the chloride (19.8 g, 85.0%) as a colourless oil (b.p.
Figure 8. 1H NMR spectrum of amine 21; ЈXЈ indicates signals
from the amine 20
the two molecules (amine 21 and phosphaneϪborane 19)
arises because the nitrogen centre inverts whereas the phos-
phorus centre does not. Working through a standard test
for diastereotopicity[26] exposes pseudoasymmetric phos-
phorus atom (this is pseudoasymmetry of the kind encoun-
tered in molecules 10 and 11)[27] upon replacement of the
methyl groups (something that does not occur with nitro-
gen). Hence, the striking contrast in the NMR spectra.
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Racemic and Enantiomerically Pure (R*,R*,R*)-Tris(α-methylbenzyl)phosphane
FULL PAPER
95 °C/20 Torr; ref.[30] 29Ϫ32 °C/0.6 Torr). Rf(EtOAc/petroleum 126.67Ϫ128.91 (several lines), 138.57 (2JP,C ϭ 4.6 Hz, i-PhCC),
ether, 1:3) ϭ 0.45. 1H NMR (400 MHz, CDCl3, 25 °C): δ ϭ 1.85 139.47 (2JP,C ϭ 4.9 Hz, i-PhCB), 139.98 (2JP,C ϭ 4.6 Hz, i-PhCA)
3
3
(d, JH,H ϭ 6.8 Hz, 3 H, CH3), 5.09 (q, JH,H ϭ 6.8 Hz, 1 H, CH)
and 7.30Ϫ7.43 (m, 5 H, 5 ϫ PhH) ppm. 13C NMR (100 MHz,
CDCl3, 25 °C): δ ϭ 26.2 (CCH3), 59.0 (CCl), 126.6 (2 ϫ o-PhC),
128.3 (p-PhC), 128.7 (2 ϫ m-PhC), 142.4 (i-PhC) ppm. EI MS:
m/z (%) ϭ 105 (100) [PhCHMe], 125 (8.8) [M35Cl Ϫ Me], 127 (2.8)
[M37Cl Ϫ Me], 140 (15.4) [M35Cl], 142 (5) [M37Cl].
ppm. 31P{1H} NMR (121 MHz, CDCl3, 25 °C): δ ϭ 51.28 ppm.
HPLC analysis of oxide 4 using a Chiracel OD column and eluting
with iPrOH/heptane (1:99) at 1 mL·minϪ1 gave retention times of
28.3 min and 43.6 min for the two enantiomers.
Attempted Reduction of Phosphane Oxide 4:[14] Phosphane oxide
(RS,RS,RS)-4 (50 mg, 0.138 mmol) was dissolved in anhydrous
THF and the solution was cooled to 0 °C. A solution of LiAlH4
(0.152 mL of a 1.0  solution in THF, 0.152 mmol) was added
dropwise and the mixture was stirred at room temperature over-
night. No reaction was evident by TLC analysis (EtOAc/petroleum
ether, 1:1). Water (10 mL) was added to the organic phase followed
by the addition of aqueous NaOH (5 mL, 20%). The organics were
extracted into EtOAc (20 mL), dried (MgSO4) and the solvents eva-
porated to dryness to give pure starting material 4 (50 mg, 100%).
In other experiments using HSiCl3 or AlH3 as the reducing agents,
starting material was also recovered.
Another reaction was conducted as above except the mixture was
heated at reflux with LiAlH4 for 2 h before being quenched by the
addition of water (10 mL) and aqueous NaOH (10 mL of a 1.5 
aqueous solution). A 1:1 mixture of starting material plus another
product was evident by TLC and 1H NMR spectroscopy. The crude
mixture was purified by flash chromatography, eluting with 50%
EtOAc/petroleum ether and graduating to 100% EtOAc to yield
the decomposition product (RS,RS)-bis(α-methylbenzyl)phos-
phane oxide (6, 34.2 mg, 48%) as a yellow oil. Rf(EtOAc, 100%) ϭ
0.15. IR (liquid film): ν˜ ϭ 2968, 2930, 2873 (CH), 2308 (PH), 1605
(Ar), 1582 (Ar), 1492, 1451 (PϪO) and 1165 (PϭO) cmϪ1. MS EI:
(RS,RS,RS)-Tris(α-methylbenzyl)phosphane Oxide (4): Freshly pre-
pared (Ϯ)-1-phenethylmagnesium chloride[10] (80 mL of a 0.45 
solution in Et2O, 36 mmol; the solution was titrated with sec-butyl
alcohol and 1,10-phenanthroline[31]) was added dropwise to a vig-
orously stirred solution of phosphorus trichloride (0.79 mL,
9.0 mmol) in anhydrous Et2O (10 mL). A white precipitate formed
almost immediately on addition. Once addition was complete, the
mixture was heated at reflux for 3 h, then cooled to room tempera-
ture and stirred overnight. The mixture was then filtered through a
frit under N2 resulting in a yellow solution. The solvent was quickly
evaporated under reduced pressure to give a yellow oil. This oil
was redissolved in CH2Cl2 (80 mL) and cold H2O2 (30%, 80 mL)
was added. The biphase was stirred vigorously for 30 min at room
temperature prior to the addition of NaOH (2 mL of an aqueous
2  solution). The resulting mixture was stirred at room tempera-
ture for a further 4 h. Water (100 mL) was added and the organics
were extracted into CHCl3 (4 ϫ 400 mL). The organic phases were
combined, dried (MgSO4) and the solvents evaporated under re-
duced pressure to give a partially solid crude yellow oil. This crude
oil was purified by flash chromatography, eluting with 10% EtOAc/
petroleum ether and graduating to 100% EtOAc, to yield a 1:1
mixture, and confirmed by the 1H NMR spectrum of (RS,RS,RS)-
tris(α-methylbenzyl)phosphane oxide (4) and (RS,RS,SR)-tris(α-
methylbenzyl)phosphane oxide (5) (1.91 g, 58.5% combined). The
two diastereoisomers 4 and 5 were separated by recrystallisation
with EtOAc to yield (RS,RS,RS)-4 as highly crystalline white
needles. M.p. 126Ϫ128 °C (from EtOAc). Rf (EtOAc/petroleum
ether, 1:1) ϭ 0.17. IR (solid state): ν˜ ϭ 2933 (CH), 1602 (Ar), 1491
and 1450 (CH deformations), and 1153 (PϭO) cmϪ1. MS EI:
m/z ϭ 362 (15) [Mϩ], 258 (19) [M Ϫ PhCHCH3ϩ], 153 (30)
m/z
ϭ ϩ
258 (15) [Mϩ], 274 (9.5) [M Oϩ], 153 (5)
[PhCH(CH3)POHϩ], and 105 (100) [PhCHCH3]. HRMS EI [Mϩ,
C16H19POϩ]: calcd. 258.117354; found 258.117004. 1H NMR
(400 MHz, CDCl3, 25 °C): δ ϭ 1.54 [dd, JP,H ϭ 15.6, JH,H
3
3
ϭ
3
3
7.3 Hz, 3 H, (CH3)A], 1.59 [dd, JP,H ϭ 17.1, JH,H ϭ 7.8 Hz, 3 H,
(CH3)B], 2.79 (quin, 2JP,H ϭ 3JH,H ϭ 7.8 Hz, the other 3JH,H coup-
2
3
ling constant ϭ 0, 1 H, CHB), 2.92 (dquin, JP,H ϭ 14.2, JH,H
ϭ
3JH,H ϭ 7.3 Hz, 1 H, CHA), 6.79 (1JP,H ϭ 450, JH,H ϭ 5.1 Hz, 1
3
H, P-H) 7.06Ϫ7.38 (m, 10 H, PhH) ppm. 13C NMR (100 MHz,
[PhCHCH3POHϩ], 105 (100) [PhCHCH3ϩ]. H NMR (400 MHz,
1
CDCl3, 25 °C): δ ϭ 15.43 [2JC,P ϭ 3.1 Hz, (CH3)B], 16.95 [2JC,P
2.3 Hz, (CH3)A], 37.81 (1JC,P ϭ 60.0 Hz, CHB), 38.18 (1JC,P
60.0 Hz, CHA), 127.43 (5JC,P ϭ 2.3 Hz, p-PhCB), 127.52 (5JC,P
ϭ
ϭ
ϭ
CDCl3, 25 °C): δ ϭ 1.29 (dd, JP,H ϭ 14.7, 3JH,H ϭ 7.5 Hz, 9 H, 3
3
2
3
ϫ CH3), 3.12 (dq, JP,H ϭ 10.3, JH,H ϭ 7.5 Hz, 3 H, 3 ϫ CH),
7.18Ϫ7.27 (m, 15 H, PhH) ppm. 13C NMR (100 MHz, CDCl3, 25
3.1 Hz, p-PhCA), 128.44 (2 ϫ o-PhCB), 128.86 (3JC,P ϭ 1.5 Hz,
2 ϫ o-PhCA), 128.92 (4JC,P ϭ 2.3 Hz, 2 ϫ m-PhC), 129.04 (4JC,P ϭ
2.3 Hz, 2 ϫ m-PhCA), 137.37 (2JC,P ϭ 5.4 Hz, i-PhCB), 138.29
(2JC,P ϭ 3.8 Hz, i-PhCA) ppm. 31P{1H} NMR (121 MHz, CDCl3,
25 °C): δ ϭ 50.43 (1JP,H ϭ 440 Hz) ppm. (RS,RS,RS)-4 (45 mg,
45.0%) was also recovered.
°C): δ ϭ 15.92 (d, JC,P ϭ 3.8 Hz, CH3), 38.9 (1JC,P ϭ 56.1 Hz,
2
CH), 126.8 (5JC,P ϭ 5.4 Hz, p-PhC), 128.5 (JC,P ϭ 2.3 Hz, m- or o-
PhC), 128.7 (JC,P ϭ 5.4 Hz, m- or o-PhC), 139.7 (2JC,P ϭ 4.6 Hz,
i-PhC) ppm. 31P{1H} NMR (121 MHz, CDCl3, 25 °C): δ ϭ
50.75 ppm. C24H27OP (362.5): calcd. C 79.53, H 7.51; found C
79.62, H 7.87. (RS,RS,SR)-Tris(α-methylbenzyl)phosphane oxide 5
was isolated as a colourless oil. Rf (EtOAc/petroleum ether, 1:1) ϭ (RS,RS,RS)-Tris(α-methylbenzyl)phosphane؊Borane (7): Phos-
0.23. IR (liquid film): ν˜ ϭ 2930 (CH), 1602 (Ar), 1492 (Ar) 1452 phorus trichloride (0.35 mL, 4.0 mmol) was suspended in anhy-
(CH deformations) and 1153 (PϭO) cmϪ1. MS EI: m/z ϭ 362 (30)
drous Et2O (10 mL) in a three-necked flask equipped with a drop-
[Mϩ], 258 (33) [(PhCHCH3)2P(O)Hϩ], 153 (38) [PhCHCH3P- ping funnel and reflux condenser and stirred vigorously. Freshly
(O)Hϩ], 105 (100) [PhCHCH3ϩ]. HRMS EI (Mϩ, C24H27POϩ):
prepared (Ϯ)-1-phenethylmagnesium chloride (40 mL of a 0.50 
calcd. 362.179954; found 362.178879. 1Η NMR (400 MHz, CDCl3, solution in Et2O, 20 mmol) was added dropwise with vigorous stir-
3
3
25 °C): δ ϭ 1.04 [dd, JP,H ϭ 14.7, JH,H ϭ 7.3 Hz, 3 H, (CH3)C], ring to the solution. A white precipitate formed immediately on
3
3
1.33 [dd, JP,H ϭ 14.7, JH,H ϭ 7.3 Hz, 3 H, (CH3)B], 1.36 [dd, addition of the Grignard. Once addition was complete, the solution
3
2
3JP,H ϭ 14.2, JH,H ϭ 7.3 Hz, 3 H, (CH3)A], 3.01 (dq, JP,H ϭ 8.3,
was heated at reflux (45 °C) for 3 h and then stirred overnight at
3JH,H ϭ 7.3 Hz, 1 H, CHC), 3.10 (dq, 2JP,H ϭ 10.7, 3JH,H ϭ 7.3 Hz, room temperature. The mixture was filtered through a frit under
2
3
1 H, CHB), 3.30 (dq, JP,H ϭ 10.3, JH,H ϭ 7.3 Hz, 1 H, CHA),
7.12Ϫ7.35 (m, 15 H, PhH) ppm. 13C NMR (100 MHz, CDCl3, 25 of BH3·THF (6 mL of a 1  solution in THF, 6.0 mmol) was added
°C): δ ϭ 14.79 [2JC,P ϭ 1.5 Hz, (CH3)C], 16.10 [2JC,P ϭ 3.81 Hz,
dropwise to the vigorously stirred solution and the resulting mix-
(CH3)B], 16.31 [2JC,P ϭ 3.8 Hz, (CH3)A], 38.16 (1JC,P ϭ 56.1 Hz, ture was stirred for a further 1 h at 0 °C. A white precipitate formed
CHC), 38.20 (1JC,P ϭ 53.8 Hz, CHB), 38.77 (1JC,P ϭ 57.7 Hz, CHA),
gradually which became yellow during this time. Cautiously the
N2 to give a pale yellow solution and was cooled to 0 °C. A solution
Eur. J. Org. Chem. 2003, 4216Ϫ4226
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4221

P. Wyatt, H. Eley, J. Charmant, B. J. Daniel, A. Kantacha
FULL PAPER
solution was added dropwise to ice-cold aqueous HCl (50 mL of
3
2
3JP,H ϭ 14.7, JH,H ϭ 7.5 Hz, 9 H, 3 ϫ CH3), 3.12 (dq, JP,H
ϭ
an aqueous 2  solution) with vigorous stirring.[32] The organic 10.3, JH,H ϭ 7.5 Hz, 3 H, 3 ϫ CH), 7.18Ϫ7.27 (m, 15 H, PhH)
3
layer was extracted with Et2O (3 ϫ 50 mL), dried (MgSO4) and the
solvents evaporated to dryness under reduced pressure yielding a
partially solid yellow oil. This crude mixture was purified using
flash chromatography, eluting with petroleum ether-EtOAc 20:1, to
ppm. 31P{1H} NMR (121 MHz, CDCl3, 25 °C): δ ϭ 50.75 ppm.
The solvent was removed under vacuum via the manifold to give
(RS,RS,RS)-tris(α-methylbenzyl)phosphane (1) as a white solid
that was stored and analysed under N2; Rf(Et2O/petroleum ether,
give
a
3:4 mixture of (RS,RS,RS)-tris(α-methylbenzyl)phos- 1:9) ϭ 0.43. 1H NMR (400 MHz, CDCl3, 25 °C): δ ϭ 1.22 (dd,
3 3
phaneϪborane (7) and (RS,RS,SR)-tris(α-methylbenzyl)phos-
phaneϪborane (19; 750 mg, 52.1%) and confirmed by 1H NMR
spectroscopy. Recrystallisation with Et2O/heptane gave pure
(RS,RS,RS)-7 as highly crystalline white needles. Rf(Et2O/petro-
leum ether, 1:20) ϭ 0.20. M.p. 162Ϫ164 °C (from Et2O/heptane).
3JP,H ϭ 11.5, JH,H ϭ 7.3 Hz, 9 H, 3 ϫ CH3), 2.95 (dq, JH,H
ϭ
2
7.1, JP,H ϭ 3.9 Hz, 3 H, 3 ϫ CH) 7.25 (m, 15 H, PhH) ppm. 13C
NMR (100 MHz, CDCl3, 25 °C): δ ϭ 19.10 (2JP,C ϭ 14.9 Hz, 3 ϫ
CH3), 35.76 (1JP,C ϭ 22.4 Hz, 3 ϫ CH), 125.6 (JP,C ϭ 2.3 Hz, p-
ArC), 127.9 (JP,C ϭ 6.2 Hz, o-ArC), 128.2 (m-ArC), 144.5 (JP,C
ϭ
IR (solid state): ν˜ ϭ 2924 and 2872 (CϪH), 2385 (BϪH), 1602 6.9 Hz, p-ArC) ppm. 31P{1H} NMR (121 MHz, CDCl3, 25 °C):
(Ar), 1491 and 1450 (CH deformations), 1377 (PB) cmϪ1. MS EI:
δ ϭ 32.76 ppm. The instability of phosphane 1 in air prevented
m/z (%) ϭ 360 (14) [M], 346 (42) [M Ϫ11BH3], 241 (40) further characterisation.
[PhCHCH3)2P], 105 (100) [PhCHCH3]. 1H NMR (400 MHz,
CDCl3, 25 °C): δ ϭ 0.30Ϫ0.90 (v br. q, 3 H, BH3), 1.13 (dd, 3JP,H ϭ
Reactions Towards Asymmetric Materials
3
2
14.7, JH,H ϭ 7.3 Hz, 9 H, 3 ϫ CH3), 2.99 (dq, JP,H ϭ 13.7,
3JH,H ϭ 6.8 Hz, 3 H, 3 ϫ CH) 7.19Ϫ7.31 (m, 15 H, PhH) ppm.
11B NMR (96 MHz, CDCl3, 1H decoupled, 25 °C): δ ϭ Ϫ45.6 (dm,
JPB ϭ 45.3 Hz) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ
18.03 (2JC,P ϭ 2.3 Hz, 3 ϫ CH3), 36.15 (1JC,P ϭ 25.4 Hz, 3 ϫ CH),
127.18 (5JC,P ϭ 2.3 Hz, p-PhC), 128.56 (JC,P ϭ 1.54 Hz, m- or o-
PhC), 128.99 (JC,P ϭ 3.8 Hz, m- or o-PhC) 140.32 (2JC,P ϭ 3.9 Hz,
i-PhC) ppm. 31P{1H} NMR (121 MHz, CDCl3, 25 °C): δ ϭ 41.0
(q, JPB ϭ 46 Hz) ppm. C24H30BP (360.2): calcd. C 80.01, H 8.39;
found C 79.88, H 8.59. (RS,RS,SR)-Tris(α-methylbenzyl)phos-
phaneϪborane (19) was isolated as a colourless oil; Rf(Et2O/petro-
leum ether, 1:20) ϭ 0.15. IR (liquid film): ν˜ ϭ 2974 and 2927, 2871
(CH), 2387 (BϪH), 1601 (Ar), 1492 (Ar), 1450 (Ar), 1384 (PB)
Synthesis of Phosphinamide Diastereomers; (R)-(anti,anti)-N-α-
Methylbenzylbis(α-methylbenzyl)phosphinic Amide (8), (R)-(anti,-
syn)-N-α-Methylbenzylbis(α-methylbenzyl)phosphinic Amide (9),
(R)-(syn-s-syn)-N-α-Methylbenzylbis(α-methylbenzyl)phosphinic
Amide (10) and (R)-(syn-r-anti)-N-α-Methylbenzylbis(α-methyl-
benzyl)phosphinic Amide (11): Phosphorus trichloride (1.71 mL,
19.6 mmol) was transferred via syringe to a dry three-necked flask
and dissolved in anhydrous Et2O (30 mL). The solution was stirred
vigorously at room temperature. (Ϯ)-1-Phenethylmagnesium chlo-
ride (81.5 mL of a 0.60  solution in Et2O, 48.9 mmol) was added
dropwise to the ethereal solution resulting in the immediate forma-
tion of a white precipitate. Once addition was complete the solution
was heated at reflux for 1 h, cooled to room temperature and fil-
tered through a frit into a dry 3-necked flask to give a pale yellow
solution. Anhydrous triethylamine (3.28 mL, 23.5 mmol) and anhy-
drous (R)-α-methylbenzylamine (99.6% ee), (2.62 mL, 20.6 mmol)
were dissolved in anhydrous Et2O (25 mL) and the mixture was
added dropwise to the pale yellow solution at room temperature
resulting in the gradual formation of a white precipitate. The solu-
tion was stirred overnight, filtered and concentrated under reduced
pressure to give a yellow oil. The oil was dissolved in CH2Cl2
(100 mL). Cold hydrogen peroxide (100 mL, 30%) was added and
the biphase was stirred vigorously for 30 min. Aqueous sodium hy-
droxide (1.8 mL of a 3  solution) was added and the solution
stirred vigorously for a further 4 h at room temperature. Water
(100 mL) was added and the aqueous layer was extracted with
CH2Cl2 (3 ϫ 100 mL). The organics were combined, dried
(MgSO4) and concentrated under reduced pressure to yield a crude
mixture of the four diastereoisomers 8؊11 (4.65 g, 62.9%) as a yel-
low-white solid. The crude solid was purified by flash chromatogra-
phy eluting with petroleum ether/EtOAc (1:1) to remove baseline
material. [Crude material gave four signals; 31P{1H} NMR
cmϪ1
. MS EI: m/z (%) ϭ 346 (4) [M Ϫ BH3], 241 (24)
[P(CHCH3Ph)2], 105 (100) [PhCHCH3]. HRMS EI [Mϩ,
C24H30BPϩ]: calcd. 360.217186; found 360.217820. 1H NMR
(400 MHz, CDCl3, 25 °C): δ ϭ 0.30Ϫ0.75 (v br. q, 3 H, BH3), 0.85
3
3
3
[dd, JP,H ϭ 14.2, JH,H ϭ 7.3 Hz, 3 H, (CH3)C], 1.40 [dd, JP,H
ϭ
12.7, 3JH,H ϭ 7.3 Hz, 3 H, (CH3)B], 1.49 [dd, 3JP,H ϭ 14.7, 3JH,H ϭ
2
3
7.4 Hz, 3 H, (CH3)A], 3.00 (dq, JP,H ϭ 14.2, JH,H ϭ 7.4 Hz, 1 H,
CHC), 3.05 (dq, 2JP,H ϭ 11.2, 3JH,H ϭ 6.8 Hz, 1 H, CHB), 3.34 (dq,
2JP,H ϭ 13.7, JH,H ϭ 7.3 Hz, 1 H, CHA), 7.18Ϫ7.37 (m, 15 H,
3
Ph-H) ppm. 11B NMR (400 MHz, CDCl3, H decoupled, 25 °C):
1
δ ϭ Ϫ43.36 ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ 15.82
[(CH3)C], 18.18 [2JC,P ϭ 2.3 Hz, (CH3)B], 18.76 [(CH3)A], 34.80
(1JC,P ϭ 23.8 Hz, CHC), 35.38 (1JC,P ϭ 15.4 Hz, CHB), 35.62
(1JC,P ϭ 14.6 Hz, CHA), 126.98 (5JC,P ϭ 1.5 Hz, p-PhCC), 127.05
(5JC,P ϭ 2.3 Hz, p-PhCB), 127.38 (5JC,P ϭ 2.3 Hz, p-PhCA),
128.10Ϫ129.18 (several lines), 139.20 (2JP,C ϭ 3.9 Hz, i-PhCC),
139.93 (2JP,C ϭ 3.1 Hz, i-PhCB) 140.70 (2JP,C ϭ 1.5 Hz,, i-PhCA)
ppm. 31P{1H} NMR (121 MHz, CDCl3, 25 °C): δ ϭ 41.95 (q,
1JPB ϭ 49.9 Hz) ppm.
(RS,RS,RS)-Tris(α-methylbenzyl)phosphane (1): (RS,RS,RS)-Tris- (123 MHz, CDCl3, 25 °C): δ ϭ 45.25, 44.66, 44.60, 43.99 ppm with
(α-methylbenzyl)phosphaneϪborane (7, 50.0 mg, 0.139 mmol) was
an integral ratio of 9:1:17:11.5 for 8/11/10/9]. Flash column chro-
dissolved in freshly distilled anhydrous diethylamine (1 mL,
matography eluting with 50% EtOAc/petroleum ether and gradu-
9.65 mmol) and heated at reflux (65 °C) under N2 for 2 h.[16,33] The ating to 100% EtOAc yielded the major isomer, pure (R)-(syn-
mixture was cooled to room temperature and de-oxygenated HCl
(5 mL of an aqueous 2  solution) was added cautiously, followed
by de-oxygenated Et2O (5 mL). The mixture was stirred vigorously
for 5 min to ensure complete extraction of the organics and the
aqueous layer was then decanted using a pipette. A portion of the
organic phase (0.5 mL) was removed and oxidised by the addition
s-syn)-10 (250 mg isolated as pure material) as a white solid. M.p.
147Ϫ149 °C (from EtOAc/petroleum ether), (ref.[20] 147.5Ϫ148 °C
from EtOAc/hexane). Rf (EtOAc, 100%) ϭ 0.18. IR (solid state):
ν˜ ϭ 3255 (NH), 2990 (CH3), 2972 (CH3), 2930 (CH), 1599 (Ar),
1208 (PϭO) cmϪ1. MS EI: m/z (%) ϭ 377 (7) [M], 272 (38) [M Ϫ
CH(CH3)Ph], 168 (48), 120 (10) [PhCH(CH3)NH] and 105 (100)
of H2O2 (2 mL, 30%) and aqueous NaOH (0.1 mL of a 1.5  aque- [PhCH(CH3)]. 1H NMR (270 MHz, CDCl3, 25 °C): δ ϭ 0.96 [d,
3
ous solution). This mixture was shaken vigorously and analysed for
3JH,H ϭ 6.9 Hz, 3 H, NHCH(CH3)Ph], 1.40 [dd, JP,H ϭ 15.5,
the presence of (RS,RS,RS)-oxide 4 which was confirmed by NMR 3JH,H ϭ 7.6 Hz, 3 H, PCH(CH3)BPh], 1.63 [dd, JP,H ϭ 15.8,
3
1
3
spectroscopy. H NMR (400 MHz, CDCl3, 25 °C): δ ϭ 1.29 (dd,
3JH,H ϭ 7.3 Hz, 3 H, PCH(CH3)APh], 1.80 (br. t, JH,H ϭ 9.6 Hz,
4222
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2003, 4216Ϫ4226

Racemic and Enantiomerically Pure (R*,R*,R*)-Tris(α-methylbenzyl)phosphane
FULL PAPER
2
3
1 H, NH), 2.96 [dq, JP,H ϭ 10.5, JH,H ϭ 7.3 Hz, 1 H, and 1147 (PϭO) cmϪ1. MS EI: m/z (%) ϭ 274 (8.5) [M], 105 (100)
PCHB(CH3)Ph], 3.15 [dq, JP,H ϭ 12.9, JH,H ϭ 7.3, 1 H, [PhCHCH3].[20] 1H NMR (400 MHz, CDCl3, 25 °C): δ ϭ 1.44 (dd,
2
3
PCHA(CH3)Ph], 4.25 [dq, JP,H ϭ 15.0, JH,H ϭ 6.9 Hz, 1 H, 3JP,H ϭ 15.6, JH,H ϭ 7.3 Hz, 6 H, 2 ϫ CH3), 2.80 (dq, JP,H
ϭ
2
3
3
2
3
NHCH(CH3)Ph], 7.02 (m, 2 H, PhH), 7.24 (m, 13 H, PhH) ppm. 12.7, JH,H ϭ 6.8 Hz, 2 H, 2 ϫ PCH), 7.16 (m, 4 H, PhH), 7.27
13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ 14.78 [PCH(CH3)BPh], (m, 6 H, PhH), 13.30 (POOH) ppm. 31P{1H} NMR (121 MHz,
15.29 [PCH(CH3)APh], 25.77 [NHCH(CH3)Ph], 38.80 [1JC,P
ϭ
CDCl3, 25 °C): δ ϭ 58.46 ppm.
76.4 Hz, PCHB(CH3)Ph], 39.84 [1JC,P ϭ 77.4 Hz, PCHA(CH3)Ph],
49.88 [NHCH(CH3)Ph], 125.84, 126.76, 126.87, 127.06, 128.22,
128.35, 128.47, 128.60, 128.64, 129.12, 139.39, 139.45, 139.50,
145.85 ppm. 31P{1H} NMR (122 MHz, CDCl3, 25 °C): δ ϭ 44.6
ppm. Fractional recrystallisation with EtOAc yielded pure (R)-
(anti,syn)-9 (600 mg) as a white solid. M.p. 210Ϫ212 °C (from
EtOAc), (ref.[20] 202Ϫ205 °C from EtOAC/hexane). Rf(EtOAc,
100%) ϭ 0.32. IR (solid state): ν˜ ϭ 3265 (NH), 3027 (CH3), 2966
(S,S)-Bis(α-methylbenzyl)phosphinic Chloride (12):[20] (S,S)-Bis(α-
methylbenzyl)phosphinic acid (13; 50.0 mg, 0.183 mmol) was dis-
solved in a 1:1 mixture of thionyl chloride and dichloromethane
(4 mL). The reagents were heated at reflux for 3 h. The reaction
was cooled and the excess thionyl chloride and CH2Cl2 were re-
moved under reduced pressure. Residual solvents and water were
removed as an azeotrope with toluene (2 ϫ 10 mL) to give the
product 12 (45.7 mg, 85.6%) as a yellow oil. Rf(Et2O/petroleum
ether, 1:1) ϭ 0.50. B.p. 240 °C/0.5 Torr.[20] 1H NMR (400 MHz,
(CH3), 2928 (CH), 2871 (CH), 1602 (Ar) and 1170 (PϭO) cmϪ1
.
MS CI: m/z (%) ϭ 378 (50) [M ϩ H], 272 (7) [M Ϫ PhCHMe], 120
(14) [PhCHMeNH], 105 (100) [PhCHMe]. 1H NMR (400 MHz,
CDCl3, 25 °C): δ ϭ 1.25 [d, 3JH,H ϭ 6.8 Hz, 3 H, NHCH(CH3)Ph],
3
3
CDCl3, 25 °C): δ ϭ 1.59 [dd, JP,H ϭ 18.6, JH,H ϭ 7.3 Hz, 3 H,
3
3
PCH(CH3)B], 1.66 [dd, JP,H ϭ 18.6, JH,H ϭ 7.4 Hz, 3 H,
2
3
PCH(CH3)A], 3.12 (dq, JP,H ϭ 8.8, JH,H ϭ 7.3 Hz, 1 H, PCHB),
3.30 (dq, 2JP,H ϭ 10.3, 3JH,H ϭ 7.4 Hz, 1 H, PCHA), 7.09 (m, 2 H,
2 ϫ PhH), 7.27Ϫ7.35 (m, 8 H, 8 ϫ PhH) ppm.[20] 13C NMR
(100 MHz, CDCl3, 25 °C): δ ϭ 136.9, 136.5, 129.32, 129.23, 129.17,
128.93, 128.5, 127.91, 127.77, 44.26 (1JC,P ϭ 66.1 Hz, PCHA), 44.73
(1JC,P ϭ 67.7 Hz, PCHB), 16.88 [2JC,P ϭ 5.4 Hz, (CH3)B], 15.37
[2JC,P ϭ 3.8 Hz, (CH3)A] ppm. 31P{1H} NMR (121 MHz, CDCl3,
25 °C): δ ϭ 76.11 ppm.
3
3
1.33 [dd, JP,H ϭ 15.6, JH,H ϭ 7.3 Hz, 3 H, PCH(CH3)BPh], 1.49
3
3
[dd, JP,H ϭ 15.2, JH,H ϭ 7.3 Hz, 3 H, PCH(CH3)APh], 1.99 [br.
t, 3JH,H ϭ 10.35 Hz, 1 H, NHCH(CH3)Ph], 2.86 [dq, 2JP,H ϭ 12.7,
3JH,H ϭ 7.8 Hz, 1 H, PCHB(CH3)Ph], 2.99 [dq, JP,H ϭ 11.2,
2
3JH,H ϭ 7.3 Hz, 1 H, PCHA(CH3)Ph], 4.42 [dq, JP,H ϭ 16.4,
2
3JH,H ϭ 7.1 Hz, 1 H, NHCH(CH3)Ph], 7.16Ϫ7.34 (m, 15 H, 15 ϫ
PhH) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ 15.1
[PCH(CH3)Ph], 16.0 [PCH(CH3)Ph], 26.4 [NHCH(CH3)Ph], 39.1
[1JC,P
ϭ
78.8 Hz, PCHB(CH3)Ph], 41.0 [1JC,P
ϭ
83.0 Hz,
PCHA(CH3)Ph], 49.76 [NHCH(CH3)Ph], 126.8, 126.9, 127.1,
128.5, 128.7 (JC,P ϭ 6.3 Hz), 129 (JC,P ϭ 7.4 Hz), 139.4 (JC,P
Methyl (S,S)-Bis(α-methylbenzyl)phosphinate (14): Anhydrous tri-
ethylamine (0.024 mL, 0.171 mmol) was added to a stirred solution
of (S,S)-13 (50 mg, 0.171 mmol) in anhydrous methanol (5 mL).
The reaction was stirred vigorously and heated at reflux for 2 h.
Water (10 mL) was added and the organics were extracted into
CH2Cl2 (2 ϫ 20 mL), dried and the solvents evaporated to dryness
under reduced pressure to give a crude yellow oil. The crude mix-
ture was purified by quick flash chromatography, eluting with 10%
EtOAc/petroleum ether and graduating to 70% EtOAc/petroleum
ether to give (S,S)-methylbis(α-methylbenzyl)phosphinate (14)
(39.0 mg, 79.2%) as a yellow oil. Rf(EtOAc/petroleum ether, 1:1) ϭ
0.26. IR (liquid film): ν˜ ϭ 3061 and 2877 (CH), 1255 (PϭO), 1022
(PϪO), 799 and 764 (Ph) cmϪ1. MS EI: m/z (%) ϭ 288 (3) [Mϩ],
105 (100) [PhCHCH3]. HRMS EI [Mϩ, C17H21PO2ϩ]: calcd.
288.127919; found 288.127777. 1H NMR (400 MHz, CDCl3, 25
ϭ
4.2 Hz), 139.5 (JC,P ϭ 6.3 Hz), 145.8 (JC,P ϭ 5.3 Hz) ppm. 31P{1H}
NMR (123 MHz, CDCl3, 25 °C): δ ϭ 44.0 ppm.[20] The third most
abundant isomer (R)-(anti,anti)-8 was successfully recrystallised
from mixed column fractions of the crude mixture, using EtOAc/
petroleum ether and isolated as a white solid. M.p. 161Ϫ163 °C
(from EtOAc/petroleum ether) (ref.[20] 161Ϫ162 °C). Rf (EtOAc) ϭ
0.24. IR (solid state): ν˜ ϭ 2978 (CH) 2933 (CH), 1492, 1451 and
1601 (Ar), 1169 (PϭO) cmϪ1. 1H NMR (400 MHz, CDCl3, 25 °C):
3
3
δ ϭ 1.17 [dd, JP,H ϭ 15.6, JH,H ϭ 7.3 Hz, 3 H, PCH(CH3)BPh],
3
3
1.35 [d, JH,H ϭ 6.8 Hz, 3 H, NHCH(CH3)Ph], 1.49 [dd, JP,H
15.6, JH,H ϭ 7.8 Hz, 3 H, PCH(CH3)APh], 2.07 [br. t, JH,H
8.8 Hz, 1 H, NHCH(CH3)Ph], 2.78 [dq, JP,H ϭ 11.2, JH,H
7.3 Hz, 1 H, PCHB(CH3)Ph], 2.92 [dq, JP,H ϭ 12.2, JH,H
ϭ
ϭ
ϭ
ϭ
ϭ
3
3
2
3
2
3
3
3
°C): δ ϭ 1.39 [dd, JP,H ϭ 16.1, JH,H ϭ 7.3 Hz, 3 H, CH(CH3)B],
3
3
3
3
7.8 Hz, 1 H, PCHA(CH3)Ph], 4.43 [br. dq, JP,H ϭ 9.8, JH,H
1.50 [dd, JP,H ϭ 15.6, JH,H ϭ 7.3 Hz, 3 H, CH(CH3)A], 2.95 (m,
2 H, 2 ϫ CH), 3.57 (d, 2JP,H ϭ 9.8 Hz, 3 H, OCH3), 7.13Ϫ7.31 (m,
10 H, PhH) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ 16.23
[2JC,P ϭ 3.1 Hz, (CH3)B], 16.25 [2JC,P ϭ 2.3 Hz, (CH3)A], 41.18
(1JC,P ϭ 41.2 Hz, CHB), 41.60 (1JC,P ϭ 43.2 Hz, CHA), 127.15 (p-
PhCB), 127.49 (p-PhCA), 128.47 (2 ϫ o-PhCB), 128.88 (2 ϫ o-
6.8 Hz, 1 H, NHCH(CH3)Ph], 6.90 (m, 2 H, PhH), 7.30 (m, 13 H,
PhH) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ 15.04
[3JC,P
ϭ
4 Hz, PCH(CH3)BPh], 16.20 [3JC,P
ϭ
4
Hz,
PCH(CH3)APh], 25.95 [NHCH(CH3)Ph], 39.60 [2JC,P ϭ 57 Hz,
PCHB(CH3)Ph], 40.10 [2JC,P ϭ 64 Hz, PCHA(CH3)Ph], 50.09
[NHCH(CH3)Ph], 125.89, 126.08, 126.76, 126.92, 127.06, 128.42,
128.44, 128.53, 128.62, 128.76, 128.81, 129.16, 129.22, 139.5, 139.6,
145.9 ppm. 31P{1H} NMR (CDCl3; 121 MHz; 25 °C): δ ϭ
45.19 ppm.
PhCA), 128.95 (4JC,P ϭ 3.1 Hz, 1 ϫ m-PhCB), 128.98 (4JC,P
ϭ
3.1 Hz, 1 ϫ m-PhCB), 129.17 (4JC,P ϭ 3.1 Hz, 1 ϫ m-PhCA), 129.20
(4JC,P ϭ 3.1 Hz, 1 ϫ m-PhCA), 138.21 (i-PhCB), 138.64 (i-PhCA)
ppm. 31P NMR (121 MHz, CDCl3, 25 °C): δ ϭ 52.58 ppm.
(S,S)-Bis(α-methylbenzyl)phosphinic Acid (13):[20] (R)-(anti,syn)-N-
Diphenylphosphinic Acid:[34] Chlorodiphenylphosphane (1.23 g,
α-Methylbenzylbis(α-methylbenzyl)phosphinic amide (9; 100 mg, 5.52 mmol) was added to water (10 mL) at room temperature with
0.265 mmol) was suspended in HCl (10 mL, of a 2  solution in
35% dioxane/water) and the mixture was heated at reflux for 2 days.
The reaction mixture was allowed to cool to room temperature and
then water (10 mL) was added. The organics were then extracted
into CH2Cl2 (3 ϫ 50 mL) and the solvents evaporated under re-
duced pressure to give a yellow oil. The crude product was washed
with cold (0 °C) pentane (2 mL) and the resulting white solid
(51.6 mg, 71.0%) was filtered and dried under vacuum to give the
pure acid 13. IR (solid state): ν˜ ϭ 2978 (CH), 1492 (Ar), 1451 (Ar)
vigorous stirring. Crushed sodium hydroxide pellets (468 mg,
11.7 mmol) were added at a rate that maintained the temperature
of the reaction below 50 °C. Immediately after the addition was
complete, aqueous hydrogen peroxide solution (0.70 mL, 30%) was
added and the mixture was stirred at 50 °C for 1 h. The mixture
was allowed to cool to room temperature and HCl (5 mL of a 2 
aqueous solution) was added. The resulting white solid was filtered.
The crude white solid was recrystallised from hot ethanol to give
pure diphenylphosphinic acid (1.03 g, 85.0%). MS EI: m/z (%) ϭ
Eur. J. Org. Chem. 2003, 4216Ϫ4226
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4223

P. Wyatt, H. Eley, J. Charmant, B. J. Daniel, A. Kantacha
FULL PAPER
218 (9) [M], 217 (23) [M Ϫ H], 77 (100) [Ph]. 1H NMR (400 MHz,
dropwise to the solution and once addition was complete, the ice
CDCl3, 25 °C): δ ϭ 7.26Ϫ7.75 (m, 10 H, ArH) ppm. 31P NMR bath was removed. The mixture was then heated at reflux for 1 h,[15]
(121 MHz, CDCl3): δ ϭ 33.78 ppm.[35]
cooled to room temperature and BH3·THF (0.441 mL of a 1.0 
solution in THF, 0.441 mmol) was added. The resulting mixture
was stirred at room temperature overnight before being quenched
by the dropwise addition of the solution to ice-cold aqueous HCl
(10 mL of an aqueous 2  solution). The organic phase was col-
lected and the aqueous phase was further extracted with Et2O
(3 ϫ 25 mL). The organic portions were combined, dried (MgSO4)
and the solvents evaporated to dryness yielding a crude white oil.
The crude oil was purified by flash chromatography, eluting
with 2% EtOAc/petroleum ether to give (S,S)-bis(α-
methylbenzyl)phosphaneϪborane (15) as a white solid (53.0 mg,
51.4%). Rf(EtOAc/petroleum ether, 1:9) ϭ 0.35. M.p. 101Ϫ103 °C
from Et2O/petroleum ether. IR (solid state): ν˜ ϭ 2970, 2931 (CH
stretch), 2399, 2386 (BH), 1599, 1489 and 1450.9 (Ar), 1375 (PB)
cmϪ1. [α]2D5 ϭ Ϫ160 (c ϭ 1.03, CH2Cl2). MS EI: m/z ϭ 256 (4.8)
[Mϩ], 242 (12.8) [M Ϫ BH3], 105 (100) [PhCHCH3]. 1H NMR
Diphenylphosphinoyl
Chloride:[36]
Diphenylphosphinic
acid
(100 mg, 0.458 mmol) was suspended in toluene (2 mL) and thionyl
chloride (0.067 mL, 0.916 mmol) was added. The mixture was
heated at reflux for 2 h, cooled to room temperature and the sol-
vent was removed under reduced pressure. Excess thionyl chloride
was removed as an azeotrope with fresh toluene (2 ϫ 2 mL) to
1
yield diphenylphosphinoyl chloride (108.3 mg, 100%) as an oil. H
NMR (400 MHz, CDCl3, 25 °C): δ ϭ 7.50Ϫ7.62 (m, 6 H, 6 ϫ
PhH), 7.91Ϫ7.85 (m, 4 H, 4 ϫ PhH) ppm. 13C NMR (100 MHz,
CDCl3, 25 °C): δ ϭ 128.85 (3JP,C ϭ 14.6 Hz, m-PhC), 131.14
(2JP,C ϭ 12.3 Hz, o-PhC), 133.13 (4JP,C ϭ 3.1 Hz, p-PhC) ppm.
31P{1H} NMR (121 MHz, CDCl3; 25 °C): δ ϭ 45.17 ppm.
Diphenylphosphane؊Borane (17). Method 1:[17] Chlorodiphenyl-
phosphane (1.00 mL, 5.57 mmol) was suspended in anhydrous
Et2O (20 mL) and the solution was cooled to 0 °C. The complex
BH3·THF (6.13 mL of a 1.0  in THF, 6.13 mmol) was added fol-
lowed by LiAlH4 (6.13 mL of a 1.0  solution in THF, 6.13 mmol)
and the mixture was stirred at 0 °C for 2 h. The solution was
quenched by addition to ice-cold aqueous HCl (25 mL of an aque-
ous 2  solution) and the organic phase was separated. The aque-
ous layer was extracted with Et2O (3 ϫ 50 mL), the organic phases
were combined, dried (MgSO4) and the solvents evaporated to dry-
ness yielding a crude white solid. The solid was purified by flash
chromatography, eluting with 5% EtOAc/petroleum ether to give
the phosphaneϪborane 17 (0.85 g, 76.3%) as a colourless oil.
Rf(EtOAc/petroleum ether, 1:9) ϭ 0.18. MS EI: m/z (%) ϭ 186 (93)
1
(400 MHz, CDCl3, 25 °C): δ ϭ 0.42Ϫ1.20 (br. q, JB,H ϭ 80 Hz, 3
H, BH3), 1.45 [dd, 3JP,H ϭ 16.9, 3JH,H ϭ 7.5 Hz, 3 H, (CH3)B], 1.55
3
3
[dd, JP,H ϭ 16.3, JH,H ϭ 7.5 Hz, 3 H, (CH3)A], 2.92 (d-quin,
2JP,H ϭ 10.1, JH,H
ϭ
3JH,H ϭ 7.4 Hz, 1 H, CHB), 3.15 (d-q-d,
3
2JP,H ϭ 14.7, 3JH,H ϭ 7.1 Hz and 3JH,H ϭ 3.3 Hz, 1 H, CHA), 4.71
(d-quin-d, 1JP,H ϭ 357.9, 3JH,H ϭ 3JH,H ϭ 6.8 Hz and 2.9 Hz, 1 H,
PH) and 7.09Ϫ7.37 (m, 10 H, ArH) ppm. 11B NMR (96 MHz,
1
1
CDCl3, H decoupled, 25 °C): δ ϭ Ϫ44.94 (br. d, JP,B ϭ 51.2 Hz)
ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ 17.77 [3JC,P
3.1 Hz, (CH3)A], 18.21 [3JC,P ϭ 1.5 Hz, (CH3)B], 32.67 (2JC,P
38.4 Hz, CHB), 33.37 (2JC,P ϭ 40.0 Hz, CHA), 127.36 (5JC,P
1.5 Hz, p-PhCB), 127.49 (5JC,P ϭ 2.3 Hz, p-PhCA), 127.78 (JC,P
ϭ
ϭ
ϭ
ϭ
3.8 Hz, o- or m-PhCB), 128.52 (JC,P ϭ 5.4, o- or m-PhCA), 128.61
(o- or m-PhCB), 128.96 (o- or m-PhCA), 140.78 (i-PhCB), 140.85 (i-
PhCA) ppm. 31P{1H} NMR (121 MHz, CDCl3, 25 °C): δ ϭ 29.8
(br. q, 1JP,B ϭ 51.2 Hz) ppm. C16H22BP (256): calcd. C 75.3, H 8.3;
found C 75.3, H 8.6.
1
[M Ϫ BH3], 108 (100) [PhP]. H NMR (400 MHz, CDCl3, 25 °C):
1
1
δ ϭ 0.70Ϫ1.40 (br. q, JB,H ϭ 84 Hz, 3 H BH3), 6.31 (dq, JP,H
ϭ
3
378.6, JH,H ϭ 6.8 Hz, 1 H, PH) and 7.44Ϫ7.70 (m, 10 H, PhH)
ppm.[17] 11B{1H} NMR (96 MHz, CDCl3, 25 °C): δ ϭ Ϫ41.3 (br.
d, JP,B ϭ 57 Hz) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ
1
126.4 (1JC,P ϭ 55.2 Hz, i-PhC), 129.13 (2JC,P ϭ 9.9 Hz, 2 ϫ o-PhC),
129.20 (p-PhC), 133.05 (3JCP ϭ 9.2 Hz, 2 ϫ m-PhC) ppm. 31P{1H} Investigating the Addition of the Third α-Methylbenzyl Unit onto the
1
NMR (121 MHz, CDCl3, 25 °C): δ ϭ 2.02 (br. q, JP,B ϭ 52 Hz)
Phosphorus Centre
ppm.
Diphenylmethylphosphane؊Borane:[17,37]
DiphenylphosphaneϪ
Diphenylphosphane؊Borane (17). Method 2: In a variation of the
above method, diphenylphosphinoyl chloride (108.3 mg,
0.458 mmol) was dissolved in anhydrous Et2O (5 mL) and the solu-
tion was cooled to 0 °C. LiAlH4 (0.450 mL of a 1  solution in
THF, 0.450 mmol) was added slowly and the mixture was heated
at reflux for 1 h,[15] cooled to room temperature, then 0 °C and the
complex BH3·THF (0.504 mL of a 1.0  solution in THF,
0.504 mmol) was added. The mixture was stirred at room tempera-
ture for 1 h and was then quenched by addition to ice-cold aqueous
HCl (10 mL of an aqueous 2  solution). The organic phase was
separated and the aqueous phase was extracted with Et2O (3 ϫ
25 mL). The organic phases were combined, dried (MgSO4) and
the solvents evaporated to dryness under reduced pressure yielding
a crude white oil. This oil was purified by flash chromatography,
eluting with 2% EtOAc/petroleum ether and graduating to 5%
EtOAc/petroleum ether to give pure diphenylphosphaneϪborane
(17) (50 mg, 54%) as a colourless oil; Rf(EtOAc/petroleum ether,
1:9) ϭ 0.18; data as above.
borane (100 mg, 0.50 mmol) and methyl iodide (0.030 mL,
0.55 mmol) were dissolved in methanol (10 mL) and the solution
was stirred at 0 °C. A solution of potassium hydroxide (0.55 mL of
a 1  solution in MeOH, 0.55 mmol) was added and the mixture
was stirred at 0 °C for 1 h followed by 1 h at room temperature.
The reaction mixture was slowly added to ice-cold aqueous HCl
(50 mL of an aqeuous 2  solution) and the organic layer was sepa-
rated. The aqueous layer was extracted with EtOAc (3 ϫ 50 mL),
the organic phases were combined, dried (MgSO4) and the solvents
evaporated to dryness yielding a crude yellow oil. The oil was puri-
fied by flash chromatography, eluting with 5% EtOAc/petroleum
ether and graduating to 10% EtOAc/petroleum ether to give
diphenylmethylphosphaneϪborane[37] (69 mg, 64.5%) as a white
solid. Rf(EtOAc/petroleum ether, 1:9) ϭ 0.19. MS EI: m/z (%) ϭ
215 (25) [M ϩ H], 200 (100) [MH Ϫ BH3]. 1H NMR (400 MHz,
1
CDCl3, 25 °C): δ ϭ 0.48Ϫ1.48 (br. q, JB,H ϭ 88.8 Hz, 3 H, BH3),
2
1.86 (d, JP,H ϭ 10.1 Hz, 3 H, PCH3), 7.50 (m, 10 H, ArH) ppm.
11B{1H} NMR (96 MHz, CDCl3, 25 °C): δ ϭ Ϫ39.29 ppm. 13C
NMR (100 MHz, CDCl3, 25 °C): δ ϭ 12.0 (1JC,P ϭ 41.2 Hz,
PCH3), 128.85 (3JP,C ϭ 14.6 Hz, m-PhC), 130.65 (1JP,C ϭ 56.9 Hz,
i-PhC), 131.17 (4JP,C ϭ 3.1 Hz, p-PhC), 131.81 (2JP,C ϭ 10.0 Hz, o-
PhC) ppm. 31P{1H} NMR (121 MHz, CDCl3, 25 °C): δ ϭ 10.69
(S,S)-Bis(α-methylbenzyl)phosphane؊Borane (15): (S,S)-Bis(α-
methylbenzyl)phosphinoyl chloride (12; 117 mg, 0.401 mmol) was
dissolved in anhydrous Et2O (5 mL) in a dry 3-neck round bot-
tomed flask. The solution was cooled to 0 °C and stirred vigor-
ously. LiAlH4 (0.401 mL of a 1.0  in THF, 0.401 mmol) was added
1
(br. q, JPB ϭ 56.6 Hz) ppm.
4224
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2003, 4216Ϫ4226

Racemic and Enantiomerically Pure (R*,R*,R*)-Tris(α-methylbenzyl)phosphane
(؎)-1-Iodo-1-phenylethane: sec-Phenethyl alcohol (10.0 mL, to Ϫ78 °C. nBuLi (0.074 mL of a 2.5  solution in hexanes,
FULL PAPER
82.9 mmol) was suspended in anhydrous dioxane (150 mL) and the
solution was vigorously stirred. Freshly distilled borontrifuoride-
diethyl etherate (10.5 mL, 82.9 mmol) was added to the solution
0.185 mmol) was added dropwise and the solution was stirred at
Ϫ78 °C for 10 min. The dry ice-acetone bath was removed and the
solution was allowed to warm to room temperature before 1-iodo-
followed by potassium iodide (41.3 g, 248 mmol) and the mixture 1-phenylethane (61.7 mg, 0.266 mmol) was added dropwise. Once
was stirred at 25 °C for 3 h. The mixture was then added to ice
cold water (100 mL) and the organics were extracted into Et2O
(3 ϫ 250 mL). The organic phases were combined, dried (MgSO4)
and the solvents evaporated to dryness to yield a crude brown oil.
This oil was immediately purified by flash chromatography, eluting
addition was complete, the reaction mixture was heated at reflux
for 1 h. The mixture was allowed to cool to room temperature and
was then quenched by the dropwise addition of it to ice-cold aque-
ous HCl (10 mL, 2 ). The organic phase was separated and the
aqueous phase was extracted with Et2O (2 ϫ 25 mL). The organic
with 1% EtOAc/petroleum ether and graduating to 2% EtOAc/ portions were combined, dried (MgSO4) and the solvents evapo-
petroleum ether. The resulting oil was washed with a solution of
sodium thiosulfate to remove iodine residues, giving the iodide
rated to dryness yielding a crude yellow oil. This oil was purified
by flash chromatography, eluting with 1% EtOAc/petroleum ether
(11.4 g, 59.2%) as a pale yellow oil. Rf(EtOAc/petroleum ether, to give a 1:1 mixture, by 1H NMR of the (S,S,S)- and (S,S,R)-
1:9) ϭ 0.78. MS EI: m/z (%) ϭ 105 (100) [M Ϫ I]. 1H NMR tris(α-methylbenzyl)phosphaneϪboranes (7) and (19) (35.0 mg,
(400 MHz, CDCl3, 25 °C): δ ϭ 2.22 (d, 3JH,H ϭ 6.8 Hz, 3 H, CH3), 54.9%) as a partially crystalline colourless oil. Flash chromatogra-
3
5.41 (q, JH,H ϭ 7.4 Hz, 1 H, CH; by contrast, the methyl and
benzylic signals are reported at 2.68 and 4.8 ppm in ref. 24.) and
7.22Ϫ7.46 (m, 5 H, ArH) ppm.[24] 13C NMR (100 MHz, CDCl3,
phy eluting with 1% EtOAc/petroleum ether gave pure (S,S,S)-
tris(α-methylbenzyl)phosphaneϪborane (7) (15.0 mg, 22.2%) as
white needles; Rf(Et2O/petroleum ether, 1:20) 0.20. Characteris-
25 °C): δ ϭ 20.02 (CH3), 26.15 (CH), 126.61 (2 ϫ o-PhC), 127.99 ation data were identical to the racemic compound except; m.p.
(p-PhC), 128.75 (2 ϫ m-PhC), 145.44 (i-PhC) ppm.
146Ϫ148 °C (from Et2O/petroleum ether). [α]2D3 ϭ Ϫ277.1 (c ϭ 1.0,
CH2Cl2). C24H30BP (360.2) calcd. C 79.8, H 8.6; found C 79.6,
H 8.2%. (S,S,R)-Tris(α-methylbenzyl)phosphaneϪborane (19) was
isolated as a colourless oil; All data as for rac-19, except HRMS
EI [Mϩ, C24H30PBϩ]: calcd. 360.217186; found 360.217820. Other
reactions that featured butyllithium and 1-phenylethyl triflate or
NaH and 1-chloro-1-phenylethane failed to give any desired prod-
uct. A reaction in which the methylation of 7 was attempted using
KOH in MeOH and methyl iodide was not successful.
(α-Methylbenzyl)diphenylphosphane؊Borane (18):
Diphenyl-
phosphaneϪborane (100 mg, 0.50 mmol) was dissolved in anhy-
drous THF (5 mL) and the solution was cooled to Ϫ78 °C. nBuLi
(0.21 mL of a 2.5  solution in hexanes, 0.525 mmol) was added
dropwise and the solution was stirred at Ϫ78 °C for 10 min. The
solution was allowed to warm to room temperature before the ad-
dition of 1-iodo-1-phenylethane (0.13 mL, 0.55 mmol). The mix-
ture was subsequently heated at reflux for 1 h. After cooling to
room temperature, the reaction was quenched by addition to ice-
cold aqueous HCl (10 mL, 2 ). The organic phase was separated
and the aqueous phase was extracted with Et2O (2 ϫ 25 mL). The
organic phases were combined, dried (MgSO4) and the solvents
evaporated to dryness yielding a crude yellow oil. This oil was puri-
fied by flash chromatography, eluting with 2% EtOAc/petroleum
ether and graduating to 5% EtOAc/petroleum ether, giving di-
phenyl-(α-methylbenzyl)phosphaneϪborane (18) (77 mg, 51%) as a
colourless oil. Rf(EtOAc/petroleum ether, 1:9) ϭ 0.19. IR (solid
(S,S,S)-Tris(α-methylbenzyl)phosphane (1): Synthesis as for (Ϯ)-1,
except
enantiomerically
pure
(S,S,S)-tris(α-methylbenzyl)-
phosphaneϪborane 7 (50.0 mg, 0.139 mmol) was used, giving
(S,S,S)-tris(α-methylbenzyl)phosphane as confirmed by 31P{1H}
NMR (121 MHz, CDCl3, 25 °C): δ ϭ 32.76 ppm. Characterisation
data were identical to (Ϯ)-1.
Crystal Data for (؊)-7: C24H30BP, M ϭ 360.26, orthorhombic, a ϭ
˚
˚
˚
6.5095(7) A, b ϭ 12.5383(13) A, c ϭ 25.999(3) A, V ϭ 2122.0(4)
3
Ϫ1
˚
A , T ϭ 100(2) K, space group P212121, Z ϭ 4 , µ ϭ 1.150 mm
;
state): ν˜ ϭ 2973, 2931, 3058, (CH), 2377 (BH stretch), 1436 (BP 4249 reflections collected, 1625 [R(int) ϭ 0.1309] independent re-
stretch) 733, 773, 680 (ArH) cmϪ1. MS EI: m/z (%) ϭ 290 (75) [M flections, R1 ϭ 0.0566 [I Ͼ 2σ(I)], wR2 ϭ 0.1271. With a Flack
Ϫ11BH3], 186 (51) [M Ϫ PhCHCH3BH3], 291 (24) [M Ϫ10BH3],
parameter of Ϫ0.09(7), the absolute stereochemistry is clearly es-
tablished and is in accord with the configuration of the starting
105 (100) [PhCHCH3]. HRMS EI [Mϩ, C20H22BPϩ]: calcd.
290.122439; found 290.122177. 1H NMR (400 MHz, CDCl3, 25 material. CCDC-208440 contains the supplementary crystallo-
1
°C): δ ϭ 0.61Ϫ1.82 (br. q, JB,H ϭ 76 Hz, 3 H, BH3), 1.58 (dd,
graphic data for this structure. These data can be obtained free of
3JP,H ϭ 16.6, 3JH,H ϭ 7.3 Hz, 3 H, CH3CH), 3.81 (dq, 2JP,H ϭ 14.7, charge via www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
3JH,H ϭ 7.4 Hz, 1 H, CH3CH) and 7.07Ϫ7.90 (m, 15 H, ArH) ppm.
Cambridge Crystallographic Data Centre, 12, Union Road, Cam-
11B{1H} NMR (96 MHz, CDCl3; 25 °C): δ ϭ Ϫ42.62 (br. d, 1JP,B ϭ bridge CB2 1EZ, UK; Fax: (internat.) ϩ44-1223-336-033; E-mail:
53 Hz) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ ϭ 16.41
deposit@ccdc.cam.ac.uk].
(CHCH3), 37.52 (2JC,P ϭ 30.3 Hz, CHCH3), 127.12 (5JC,P
ϭ
Crystal Data for (؎)-7: C24H30BP, M ϭ 360.26, monoclinic, a ϭ
2.3 Hz, p-PhCBn), 127.89 (JC,P ϭ 2.3, o- or m-PhCBn), 128.15
(3JC,P ϭ 10.0 Hz, m-PhAC), 128.82 (3JC,P ϭ 10.0 Hz, m-PhBC),
129.32 (JC,P ϭ 4.6 Hz, o or m-PCBn), 129.70 (1JC,P ϭ 58.0 Hz, i-
PhBC), 130.20 (1JC,P ϭ 50.0 Hz, i-PhAC), 130.81 (4JC,P ϭ 2.3 Hz,
p-PhBC), 131.36 (4JC,P ϭ 2.3 Hz, p-PhAC), 132.87 (2JC,P ϭ 8.5 Hz,
o-PhBC), 133.10 (2JC,P ϭ 8.5 Hz, o-PhAC), 137.9 (i-PhCBn) ppm.
31P{1H} NMR (121 MHz, CDCl3, 25 °C): δ ϭ 26.24 (br. q, 1JB,P ϭ
53 Hz) ppm. Another reaction involving KOH in methanol and 1-
chloro-1-phenylethane was attempted and found to be unsuccess-
ful.
˚
˚
˚
14.3470(3) A, b ϭ 12.4544(2) A, c ϭ 12.9509(3) A, V ϭ 2093.35(7)
3
Ϫ1
˚
A , T ϭ 150(2) K, space group P21/c, Z ϭ 4 , µ ϭ 1.165 mm
;
12324 reflections collected, 2869 [R(int) ϭ 0.0295] independent re-
flections, R1 ϭ 0.0424 [for 2541 reflections with I Ͼ 2σ(I)], wR2 ϭ
0.1368. CCDC 211488 contains the supplementary crystallographic
data for this structure.
Crystal Data for (؎)-4: C24H27OP, M ϭ 362.43, triclinic, a ϭ
3
˚
˚
˚
˚
5.7141(11) A, b ϭ 10.803(2) A, c ϭ 16.485(3) A, V ϭ 984.5(3) A ,
T ϭ 173(2) K, space group P1, Z ϭ 2 , µ ϭ 0.149 mmϪ1; 10045
¯
reflections collected, 4465 [R(int) ϭ 0.0495] independent reflec-
(S,S,S)-Tris(α-methylbenzyl)phosphane؊Borane (7): (S,S)-Bis(α-
methylbenzyl)phosphaneϪborane (7) (45.0 mg, 0.177 mmol) was
dissolved in anhydrous THF (5 mL) and the solution was cooled
tions, R1 ϭ 0.0475 [for 2859 reflections with I Ͼ 2σ(I)], wR2 ϭ
0.0954. CCDC-211487 contains the supplementary crystallographic
data for this structure.
Eur. J. Org. Chem. 2003, 4216Ϫ4226
www.eurjoc.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4225

P. Wyatt, H. Eley, J. Charmant, B. J. Daniel, A. Kantacha
FULL PAPER
[17]
[18]
[19]
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Am. Chem. Soc. 1990, 112, 5244Ϫ5252.
K. M. Pietrusiewicz, M. Zablocka, Chem. Rev. 1994, 94,
1375Ϫ1411.
H. C. Brown, J. R. Schwier, B. Singaram, J. Org. Chem. 1978,
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Acknowledgments
The generous support of the School of Chemistry is gratefully
acknowledged. H. E. is supported by the EPSRC.
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