Stereoselective hydrosilylation of enals and enones catalysed by palladium nanoparticles

Article abstract of DOI:10.1002/chem.201100655

A highly versatile and efficient hydrosilylation method by palladium nanoparticle catalysis allows the direct and chemoselective synthesis of 1)enolsilanes of high isomeric purity, 2)saturated aldehydes or ketones, or 3)the corresponding saturated acetals from α,β-unsaturated aldehydes or ketones. The choice of the product is determined by simply switching the solvent from THF to mixtures of THF/water or THF/alcohol. Copyright

Full text of DOI:10.1002/chem.201100655

DOI: 10.1002/chem.201100655
Stereoselective Hydrosilylation of Enals and Enones Catalysed by Palladium
Nanoparticles
Meryem Benohoud, Sakari Tuokko, and Petri M. Pihko*[a]
Abstract: A highly versatile and efficient hydrosilylation method by palladium
nanoparticle catalysis allows the direct and chemoselective synthesis of 1) enolsi-
Keywords: acetals
heterogeneous catalysis · hydrosily-
lation · nanoparticles · palladium
· aldehydes ·
lanes of high isomeric purity, 2) saturated aldehydes or ketones, or 3) the corre-
sponding saturated acetals from a,b-unsaturated aldehydes or ketones. The choice
of the product is determined by simply switching the solvent from THF to mix-
tures of THF/water or THF/alcohol.
Introduction
Stereo- and chemoselective reductions of a,b-unsaturated
carbonyl compounds are highly important reactions in or-
ganic synthesis[5] due to the high utility of stereodefined
enolsilanes as nucleophiles. 1,4-Hydrosilylation of enals and
enones with modest stereoselectivities has been achieved
with a number of metal catalysts, including copper,[6] palladi-
um,[7] rhodium[8] and others.[9] Surprisingly, heterogeneous or
nanoparticle catalysis with palladium has not been explored,
although the presence of a reducing agent, such as a silane,
and a reducible metal complex might readily lead to the for-
mation of metallic (nano)particles that could act as the true
catalysts.[10]
The advantages of nanoparticles as catalysts are typically as-
sociated with their high efficiency in traditional reactions,
such as oxidation and reduction, or as reservoirs of metals
for homogeneous reactions.[1] However, stereoselective reac-
tions catalysed by nanoparticles are still quite rare,[2] the
substrate scopes of the reactions are often very limited[3]
and, in many cases, these reactions have turned out to be
catalysed by leached catalyst species in the solution phase.[4]
Herein, we report that palladium nanoparticles (PdNPs)
can be used in a highly stereoselective hydrosilylation of un-
saturated enals and enones catalysed by PdNPs with a wide
substrate scope. By changing the composition of the solvent
mixture of the reaction, it is also possible to access saturated
aldehydes, ketones or acetals (Scheme 1).
Results and Discussion
Highly stereoselective 1,4-hydrosilylation of enals and
enones: We initiated our study with the palladium-catalysed
hydrosilylation of a-substituted acroleins. These compounds
are efficiently prepared by a-methylenation of aldehydes.[11]
The a-benzyl acrolein 1a was subjected to the optimised
conditions described in the literature for the 1,4-hydrosilyla-
tion of enones.[8,12] Promising results were obtained with Pd-
AHCTUNTGRENGUN(N OAc)2 and tricyclohexylphosphine (PCy3); a catalyst combi-
nation described by Oshima et al. for the stereoselective 1,4-
hydrosilylation of a,b-unsaturated ketones,[13] allowing us to
isolate the desired enolsilane as a single Z isomer with a
conversion of 63% (Table 1, entry 1). Superior yields and
faster conversions were obtained with the PdCl2/PCy3 cata-
lyst system (Table 1, entry 3). A solvent screen indicated
THF as the optimal solvent; this allowed us to reduce the
loading of silane to 110 mol% and significantly assisted the
purification of the products.[14] The excellent results ob-
tained with this catalyst system for a-benzyl acrolein (100%
conversion in 3 h, 84% isolated yield, >50:1 Z/E selectivity;
Table 1, entry 3) encouraged us to test the generality of this
protocol with a range of unsaturated carbonyl compounds.
The results of the hydrosilylation experiments under opti-
mised conditions are summarised in Table 2. The reaction
Scheme 1. Three optional reactivity modes for the hydrosilylation of
enals and enones with PdNPs.
[a] Dr. M. Benohoud, S. Tuokko, Prof. Dr. P. M. Pihko
Nanoscience Center and Department of Chemistry
University of Jyvꢀskylꢀ
P. O. B. 35 FI-40014 JYU (Finland)
Fax : (+358) 14 260 2501
E-mail: Petri.Pihko@jyu.fi
Homepage: http://www.jyu.fi/kemia/tutkimus/orgaaninen/en/research/
Pihko
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100655.
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FULL PAPER
Table 1. Screening of the catalytic system.
activity is not restricted to cata-
lysts prepared with silane re-
duction, we also prepared
poly(N-vinyl-2-pyrrolidone)
(PVP)-stabilised
PdNPs.[20]
Entry
Catalyst
Conditions[a]
Conv.[b]
[%]
Z/E[c]
These PVP-stabilised PdNPs
are also active catalysts for hy-
drosilylation, affording the
same stereoselectivity for 2a
(>25:1 Z/E ratio) as our own in
situ prepared PdNP catalyst,
but with a lower chemoselectiv-
ity and reaction rate.[14] Al-
M [mol%]
L [mol%]
Solvent
T
t [h]
1
2
3
4
Pd
Pd
N
5.0
1.5
1.5
1.5
10.0
3.0
3.0
toluene
THF
THF
RT
RT
RT
RT
14
3
3
63[d]
50
>50:1
>50:1
>50:1
>50:1
PdCl2/PCy3
PdCl2/PPh3
>95[d]
20
3.0
THF
3
[a] M=metal, L=ligand. [b] The conversion was measured by GC. [c] The stereoselectivity was measured by
1H NMR spectroscopy. [d] Traces of saturated aldehyde (5–10%) were also detected.
affords excellent stereoselectivities with a-monosub-
Table 2. Hydrosilylations of unsaturated aldehydes and ketones using the PdCl2/PCy3
catalytic system.
stituted enals (Table 2, entries 1–9), b-monosubstitut-
ed enals (Table 2, entries 10–12), as well as b,b-disub-
stituted enals (Table 2, entries 13–16) with alkyl or
substituted alkyl substituents. For aldehydes with b-
aryl groups, the reaction is not chemoselective. In
these cases, the major product is the 1,2-hydrosilyla-
tion product.[15] However, cyclic and acyclic enones
readily participate in the reaction without chemose-
lectivity problems (Table 2, entries 19 and 20).
Enal/Enone
Product
Yield[a] Z/E[b]
[%]
Investigating the nature of the real catalyst: The for-
mation of the Z isomer in the hydrosilylation reac-
tion is not directly reconcilable with the mechanism
proposed by Oshima and co-workers.[16] To shed light
on the mechanism, kinetic studies were initiated. Al-
though the reactions were typically completed within
1–2 h, an induction period was always observed and
the rates did not show a clear dependence on the
concentration of either substrate. We therefore sus-
pected that the catalytically active black reaction
mixture generated after addition of triethylsilane
may not be a homogeneous system.[17] Additionally,
we observed the slow deposition of black particles
on the bottom of the reaction vessel. Centrifugation
of the reaction mixture allowed us to separate the
particles from the solution. After washing with THF,
the re-suspended particles were still active hydrosily-
lation catalysts for up to six recycles.[14] Importantly,
the supernatant liquor still contained some palladi-
um (35 mgLÀ1), but it was no longer an active cata-
lyst.[14] These experiments confirmed the heterogene-
ity of the catalytic system.[18]
The TEM images of palladium particles formed in
situ and isolated after completion of the hydrosilyla-
tion reaction and those of palladium particles
formed ex situ are comparable. The particles are 6 to
9 nm in scale, but readily form aggregates (Figure 1).
The isolated particles are still active in hydrosilyla-
tion and they display catalytic activity similar to that
observed for related PdNPs. For example, they are
active catalysts for hydrogenolysis and hydrogena-
tion reactions.[19] To confirm that the hydrosilylation
1
84
>50:1
2
3
4
98
93
81
20:1
>50:1
20:1
5
6
85
84
>50:1
20:1
7
8
9
84
86
86
>50:1
>50:1
13:1
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P. M. Pihko et al.
Saturated aldehydes or ketones under aqueous
conditions: The scope of the hydrosilylation is not
restricted to nonaqueous conditions and the nano-
particles retain their activity in water. As such,
when the hydrosilylation is performed in aqueous
THF, saturated aldehydes or ketones are generat-
ed rapidly (Table 3). A control experiment with
the enolsilane 2a indicated that the enolsilane is
stable under the reaction conditions,[14] and there-
fore, it appears likely that the saturated aldehydes
and ketones are generated directly in the process
in the presence of water. Furthermore, the reac-
tions are significantly accelerated in the presence
of water when compared with nonaqueous condi-
tions.[14]
The scope of the reduction under aqueous con-
ditions was screened with different a-substituted
acroleins (Table 3, entries 1–5), b-substituted enals
(Table 3, entries 6 and 7) and a,b-disubstituted
enal (Table 3, entry 8) as well as both aliphatic
and aromatic ketones (Table 3, entries 9 and 10).
Importantly, this reduction proceeds under mild
conditions (RT) and typically takes only 1 h to
complete, affording the products cleanly. No 1,2-
reduction products were detected; even chalcone
1v afforded clean 1,4-reduction. The reactions can
also be readily scaled up: the reduction of 1a at
the 10 mmol scale affords 3a in 93% yield
(1.37 g).[22]
Table 2. (Continued)
Enal/Enone
Product
Yield[a] Z/E[b]
[%]
10
11
94
87
>1:50
>1:50
12
13
83
90
1:12
>1:50
14
95
>1:50
15
16
96
99
1:10
1:10
Direct formation of acetals with alcohols: Finally,
by using methanol or ethylene glycol as the co-sol-
vent instead of water, the corresponding saturated
acetals can be accessed directly (Table 4). The for-
mation of acetals is attributed to traces of HCl
generated during the PdNP formation.[23] The con-
ditions are mild enough to preserve potentially
labile protecting groups, such as cyclic acetals
(Table 4, entry 3) or Boc groups (Table 4, entry 5).
For all of the substrates tested (Table 4), the reac-
tion was completed after only 15–30 min and af-
forded an essentially pure acetal; the only signifi-
cant side products were the silylated alcohols
(e.g., Et3SiOCH2CH2OH). For both aldehydes and
ketones, this protocol affords the saturated acetals
rapidly and in high yields.
17
18
82
88
7:1
N/A
19
20
95
91
1:3
N/A
Mechanistic aspects: The high stereoselectivities
obtained in this process and the (seemingly) oppo-
site stereoselectivities obtained with a- and b-sub-
stituted enals suggest that the mechanism may in-
volve a selective trapping of the s-trans conforma-
tion of the enal with the hydrosilylating catalyst,
[a] Yields of isolated product. [b] Stereoselectivity measured by 1H NMR spectrosco-
py.
though the PdNPs prepared by the silane reduction can be
separated and recycled, we recommend in situ preparation
for the hydrosilylation reaction for convenience and the best
yields.[21]
resulting in an enolsilane in which the hydride-bearing
carbon and the enolate are trans to each other. This is the
pattern universally observed in the hydrosilylations. Further-
more, the results under aqueous conditions indicate that the
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Stereoselective Hydrosilylation of Enals and Enones
FULL PAPER
Table 3. Reduction of unsaturated carbonyl compounds to saturated car-
bonyls under aqueous conditions.
Entry
1
Enal/Enone
Product
Yield[a] [%]
93
Figure 1. TEM images showing aggregated PdNPs.[15,22]
2
3
84
78
reaction is likely to proceed by a “hydride first” type mecha-
nism and protonation of the intermediate enolate proceeds
faster than its silylation. Otherwise, the enolsilanes would
accumulate in the reaction mixture, since they are stable to
the reaction conditions. Finally, any explanation for the se-
lectivity must account for the result that differently pre-
pared PdNPs (see above) display similar stereoselectivities.
A possible rationalisation for these results consistent with
these observations is presented in Scheme 2. The mechanism
is believed to be initiated from a PdNP complex of the enal.
In the proposed mechanism, the initial hydropalladation
step is followed by irreversible O-silylation of the O-bound
Pd enolate,[24] trapping the product as a (Z)-enolsilane (a-
substituted enals) or (E)-enolsilane (b-substituted enals).
The role of the PdNPs in this scenario is to facilitate hydro-
palladation in the s-trans conformation of the enal. This pro-
cess might be difficult with a mononuclear Pd species for
steric reasons, but could be readily achieved with a nanopar-
ticle because two different Pd atoms could be involved in
4
5
84
87
6
7
92
93
À
hydride delivery and the formation of the Pd O bond.
8
87
Under aqueous conditions, the palladium enolate species
could then be readily protonated, affording the saturated
products 3.
In further support of the proposed mechanism, a competi-
tion experiment with Et3SiD and Ph3SiH was carried out
(Scheme 2c). The differently silylated products 2a and 2a’
were generated with good stereoselectivity and in a 1:1
ratio. However, both products were deuterated to a similar
extent, indicating full and reversible cleavage of the silanes
prior to the hydrosilylation event.
9
91
94
10
[a] Yield of isolated product.
Finally, in the presence of alcohols, the formation of satu-
rated acetals is likely to proceed by an acid-catalysed acetal-
isation. Indeed, when a 1:1 mixture of cyclohexenone 1u
and 4-methylcyclohexanone were subjected to the reaction
conditions with ethylene glycol, 4-methylcyclohexanone was
also acetalised at a rate comparable to the formation of 4u
(see Supporting Information).
Conclusion
We have developed a stereoselective PdNP-catalysed hydro-
silylation method for enals and enones with the following
useful features: 1) the reduction can be performed chemose-
lectively in the presence of other potentially reducing
groups, such as nitro compounds or other C=C bonds;
2) conjugate reduction affords highly versatile nucleophiles,
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P. M. Pihko et al.
Table 4. Reduction of unsaturated carbonyl compounds to saturated ace-
tals under mixed solvent conditions.[a]
Entry
1
Enal/Enone
Product
Yield[b] [%]
95
2
3
93
81
4
5
93
95
6
7
89
94
Scheme 2. Rationalisation for the observed stereoselectivity starting from
hydrosilylated PdNPs.
the 1,4-reduction. Finally, the active catalytic species have
been identified as PdNPs formed in situ, expanding the
scope of PdNP catalysis to hydrosilylations of enones and
enals. Further mechanistic studies, as well as studies on the
scope of the transformation, are underway.
8
98
[a] Boc=tert-butyloxycarbonyl. [b] Yield of isolated product.
Experimental Section
General: All reactions were conducted in screw-cap glass vials. The vials
were used without drying.
THF, dichloromethane, acetonitrile and toluene used were obtained by
passing deoxygenated solvents through activated alumina columns
(MBraun SPS-800 Series solvent purification system). Other solvents and
reagents were used as supplied, unless otherwise noted.
such as enolsilanes or metal enolates as intermediates and
3) the conjugate reduction of the C=C bond activates the
C=O bond towards nucleophilic attack, such as acetal for-
mation. The method reported herein allows a very conven-
ient access to enolsilanes, saturated aldehydes or ketones, or
their acetals in high yields by using a single nanoparticle cat-
alyst system. The choice of the product is determined by
simply switching the solvent from THF to THF/water or
THF/alcohol mixture. The products were obtained in high
yields and in most cases the enolsilanes were obtained with
excellent stereoselectivities. The good isomeric purity of the
enolsilanes should be useful for a range of further transfor-
mations, and with the exception of cinnamaldehyde deriva-
tives, all reduction reactions are highly chemoselective for
Analytical TLC was performed by using Merck silica gel F254 (230–400
mesh) plates and analysed by UV light (254 or 366 nm) and by staining
upon heating with standard vanillin, permanganate, ninhydrin or phos-
phomolybdic acid solutions. For silica-gel chromatography, the flash chro-
matography technique was used, with Merck silica gel 60 (230–400 mesh)
and p.a. grade solvents unless otherwise noted. GC analyses were per-
formed with an Agilent Technologies 7890GC instrument equipped with
an Agilent HP-5 capillary column (30ꢂ0.320ꢂ0.25 mm). Dibenzyl ether
was used as the internal standard. IR spectra were recorded on a Bruker
TENSOR27 FTIR spectrometer. Optical rotations were recorded on a
Perkin–Elmer 341B polarimeter using a sodium lamp (D line). 1H and
13C NMR spectra were recorded in CDCl3 on Bruker Avance 250 and
500 spectrometers. The chemical shifts are reported in ppm relative to
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Stereoselective Hydrosilylation of Enals and Enones
FULL PAPER
CHCl3 (d=7.26 ppm for 1H and d=77.2 ppm for 13C NMR spectroscopy).
High-resolution mass spectrometric data were obtained with a QSTAR
Elite MS/MS system by the Analytical Services of the Department of
Chemistry at the University of Jyvꢀskylꢀ.
Compound 2d: Enolsilane 2d was obtained from acrolein 1d (100 mg,
0.62 mmol) as a 20:1 mixture of Z/E isomers as a colourless oil (140 mg,
81%). H NMR (250 MHz, CDCl3): d=0.65–0.75 (m, 6H; 3ꢂCH2), 1.00–
1
1.05 (m, 9H; 3ꢂCH3), 1.66 (s, 3H; CH3), 5.01 (s, 2H; CH2), 5.67 (brs,
1H; CH), 7.29–7.45 ppm (m, 5H; 5ꢂCH); 13C NMR (63 MHz, CDCl3):
d=4.7, 6.8, 16.0, 71.3, 122.9, 127.6, 127.8, 128.4, 137.1, 139.0 ppm; IR
(neat): 2954, 2876, 1728, 1068, 1003, 728, 695 cmÀ1; MS (ES+): 278 [M],
249 [MÀEt], 191 [MÀEt3], 163 [MÀSiEt3], 115 [SiEt3].
General procedure for catalytic system screen (Table 1, entry 1): Acrolein
1a (50 mg, 0.34 mmol, 100 mol%) and triethylsilane (65 mL, 0.68 mmol,
200 mol%) were added to a mixture of Pd
5 mol%) and PCy3 (9.5 mg, 0.034 mmol, 10 mol%) in toluene (1.1 mL,
(acrolein) =0.3m) at 08C. The reaction mixture was stirred at RT for 14 h,
ACHTUNGRTEN(NUNG OAc)2 (3.8 mg, 0.017 mmol,
Compound 2e: Enolsilane 2e was obtained from acrolein 1e (100 mg,
c
1
0.58 mmol) as the Z isomer as a light yellow oil (142 mg, 85%). H NMR
then filtered through a pad of alumina and washed with hexanes. After
evaporation of the solvents, the material was purified by flash chromatog-
raphy (silica gel, hexanes). The desired product was isolated as a colour-
less oil (56 mg, 63%).
(250 MHz, CDCl3): d=0.60–0.70 (m, 6H; 3ꢂCH2), 0.91–1.00 (m, 9H; 3ꢂ
CH3), 1.45 (s, 9H; 3ꢂCH3), 1.93 (d, J=2.0 Hz, 3H; CH3), 5.55 (brs, 1H;
CH), 6.31 ppm (brs, 1H; NH); 13C NMR (63 MHz, CDCl3): d=4.6, 6.7,
15.1, 28.6, 79.7, 118.1, 123.0, 153.2 ppm; IR (neat): 3347, 2955, 2877, 1697,
1367, 1150, 1065, 1004, 728 cmÀ1; MS (ESI+): 311.2 [M+H+Na], 326.2
[M+H+K].
General procedure for catalytic system screen (Table 1, entries 2–4):
Acrolein 1a (50 mg, 0.34 mmol, 100 mol%) and triethylsilane (59 mL,
0.37 mmol, 110 mol%) were added to a suspension of PdACTHUNRGTNEUNG(OAc)2 (1.1 mg,
0.005 mmol, 1.5 mol%) or PdCl2 (0.9 mg, 0.005 mmol, 1.5 mol%) and
PCy3 (2.8 mg, 0.010 mmol, 3.0 mol%) or PPh3 (2.6 mg, 0.010 mmol,
3.0 mol%) in THF (c(acrolein) =0.3m). The reaction mixture was stirred at
RT for 3 h. GC analyses of the reaction mixture were performed with ali-
quots filtered through a short pad of alumina to remove traces of the cat-
alyst. The alumina pad was washed with CH2Cl2 (1 mL).
Compound 2 f: Enolsilane 2 f was obtained from acrolein 1 f (37 mg,
0.20 mmol) as a 20:1 mixture of Z/E isomers as a colourless oil (50 mg,
1
84%). [a]D =+4.3 (c=0.90 in CH2Cl2); H NMR (250 MHz, CDCl3): d=
0.59–0.69 (m, 6H; 3ꢂCH2), 0.85–0.99 (m, 15H; 5ꢂCH3), 1.57 (s, 3H;
CH3), 1.61–1.73 (m, 4H; 2ꢂCH2), 3.55 (t, J=8.5 Hz, 1H; CH(H)), 3.99
(t, J=7.5 Hz, 1H; CH(H)), 5.24 (dd, J=6.5, 9.0 Hz, 1H; CH), 6.20 ppm
(s, 1H; CH); 13C NMR (63 MHz, CDCl3): d=4.6, 6.7, 8.2, 8.4, 12.2, 29.8,
General procedure for the preparation of enolsilanes: The acrolein
(0.50 mmol, 100 mol%) and the triethylsilane (89 mL, 0.55 mmol,
110 mol%) were added to a suspension of PdCl2 (1.3 mg, 0.0075 mmol,
1.5 mol%) and PCy3 (4.2 mg, 0.015 mmol, 3.0 mol%) in dry THF
(c(acrolein) =0.3m). The reaction mixture was stirred at RT. After 5 min, the
mixture became dark (black or brown). The reaction could be followed
by TLC (eluent: hexanes/ethyl acetate 9:1) or by GC. After completion
of the reaction (3 h on average), the mixture was filtered through a pad
of alumina (2ꢂ2 cm), eluted with hexanes (2ꢂ10 mL) and concentrated
in vacuo. The residue was purified by flash chromatography (silica gel,
hexanes or hexanes/diethyl ether 99:1) to afford the pure products.
30.0, 67.3, 72.3, 112.3, 113.3, 137.7 ppm; IRACTHUNRGTNEUNG(neat): 2941, 2880, 1722, 1075,
916, 731 cmÀ1; HRMS (ESI+): m/z calcd for C16H32O3SiNa: 323.2018;
found: 323.2009.
Compound 2g: Enolsilane 2g was obtained from acrolein 1g (50 mg,
0.31 mmol) as the Z isomer as a colourless oil (72 mg, 84%). 1H NMR
(250 MHz, CDCl3): d=0.73 (q, J=8.0 Hz, 6H; 3ꢂCH2), 1.05 (t, J=
8.0 Hz, 9H; 3ꢂCH3), 1.38 (s, 3H; CH3), 1.39 (d, J=7.4 Hz, 3H; CH3),
4.40 (q, J=7.4 Hz, 1H; CH), 6.14 (brs, 1H; CH), 7.16 (m, 1H; CH),
7.31 ppm (d, 4H; 4ꢂCH); 13C NMR (63 MHz, CDCl3): d=4.8, 6.8, 13.3,
16.9, 35.8, 120.6, 125.7, 127.6, 128.1, 133.5, 145.6 ppm; IR (neat): 2958,
2877, 1150, 697 cmÀ1
; HRMS (ESI+): m/z calcd for C17H28OSiNa:
Compound 2a: Enolsilane 2a was obtained from acrolein 1a (50 mg,
0.34 mmol) as the Z isomer as a colourless oil (75 mg, 84%). Rf =0.93
(hex); 1H NMR (250 MHz, CDCl3): d=0.74 (q, J=8.0 Hz, 6H; 3ꢂCH2),
1.06 (t, J=8.0 Hz, 9H; 3ꢂCH3), 1.50 (d, J=1.5 Hz, 3H; CH3), 3.48 (s,
2H; CH2), 6.25 (d, J=0.8 Hz, 1H; CH), 7.18–7.34 ppm (m, 5H; 5ꢂCH);
13C NMR (63 MHz, CDCl3): d=4.8, 6.8, 17.1, 35.2, 116.0, 125.7, 128.3,
129.0, 134.4, 141.3 ppm; IR (neat): 2956, 2877, 1672, 1454, 1181, 1136,
1005, 825, 727, 618 cmÀ1; HRMS (ESI+): m/z calcd for C16H26OSiNa:
285.1651; found: 285.1651.
299.1807; found: 299.1801.
Compound 2h: Enolsilane 2h was obtained from acrolein 1h (42 mg,
0.30 mmol) as the Z isomer as a colourless oil (66 mg, 86%). 1H NMR
(250 MHz, CDCl3): d=0.59–0.69 (m, 6H; 3ꢂCH2), 0.86–0.91 (m, 3H;
CH3), 0.95–1.01 (m, 9H; 3ꢂCH3), 1.27–1.39 (m, 8H; 4ꢂCH2), 1.50 (d,
J=1.3 Hz, 3H; CH3), 2.08 (t, J=7.0 Hz, 2H; CH2), 6.06 ppm (brs, 1H;
CH); 13C NMR (63 MHz, CDCl3): d=4.8, 6.8, 14.3, 17.3, 22.9, 27.5, 28.7,
29.4, 32.1, 117.5, 133.5 ppm; IR (neat): 2955, 1159, 1004, 823, 720 cmÀ1
HRMS (ESI+): m/z calcd for C15H33OSi: 257.2301; found: 257.2306.
;
Compound 2a’: Enolsilane 2a’ was obtained from acrolein 1a (50 mg,
0.34 mmol) as the Z isomer as a white semi-solid (119 mg, 86%). M.p.
96.4–97.88C; 1H NMR (250 MHz, CDCl3): d=1.43 (d, J=1.5 Hz, 3H;
CH3), 3.57 (s, 2H; CH2), 6.31 (brs, 1H; CH), 7.16–7.24 (m, 5H; 5ꢂCH),
7.37–7.48 (m, 9H; 9ꢂCH), 7.64–7.68 ppm (m, 6H; 6ꢂCH); 13C NMR
(63 MHz, CDCl3): d=17.1, 35.5, 117.4, 125.8, 128.2, 128.4, 129.1, 130.5,
Compound 2i: Enolsilane 2i was obtained from acrolein 1i (100 mg,
0.61 mmol) as a 13:1 mixture of Z/E isomers as an orange oil (147 mg,
86%). H NMR (250 MHz, CDCl3): d=0.70 (q, J=8.0 Hz, 6H; 3ꢂCH2),
1.02 (t, J=8.0 Hz, 9H; 3ꢂCH3), 1.29 (d, J=7.3 Hz, 3H; CH3), 1.40 (d,
J=1.5 Hz, 3H; CH3), 2.26 (s, 3H; CH3), 4.29 (q, J=7.3 Hz, 1H; CH),
5.84–5.88 (m, 2H; 2ꢂCH), 6.13 ppm (brs, 1H; CH); 13C NMR (63 MHz,
CDCl3): d=4.7, 6.8, 13.3, 13.7, 16.2, 30.9, 105.0, 105.7, 118.7, 134.0, 150.2,
157.4 ppm; IR (neat): , 2877, 1716, 1458, 1005, 824, 728 cmÀ1; HRMS
(ESI+): m/z calcd for [C16H28OSiNa]: 303.1756; found: 303.1743.
1
133.6, 134.0, 135.6, 140.8 ppm; IR (neat): 3068, 3024, 2851, 695, 518 cmÀ1
;
HRMS (ESI+): m/z calcd for C28H26OSiNa: 429.1651; found: 429.1661.
Compound 2b: Enolsilane 2b was obtained from acrolein 1b (100 mg,
0.60 mmol) as a 20:1 mixture of Z/E isomers as a colourless oil (165 mg,
98%). [a]D =+1.7 (c=1.00, CH2Cl2); 1H NMR (250 MHz, CDCl3): d=
0.61–0.70 (m, 6H; 3ꢂCH2), 0.94–1.03 (m, 12H; 4ꢂCH3), 1.26–1.38 (m,
2H; CH2), 1.40 (d, J=1.5 Hz, 3H; CH3), 1.59 (s, 3H; CH3), 1.68 (s, 3H;
CH3), 1.92 (q, J=7.5 Hz, 2H; CH2), 2.93 (sextet, J=7.0 Hz, 1H; CH),
5.13–5.19 (m, 1H; CH), 6.06 ppm (s, 1H; CH); 13C NMR (63 MHz,
CDCl3): d=4.8, 6.8, 12.7, 17.7, 18.8, 25.9, 26.6, 30.6, 35.0, 120.7, 125.5,
130.9, 133.4 ppm; IR (neat): 2957, 1146, 729 cmÀ1; HRMS (ESI+): m/z
calcd for C17H34OSiNa: 305.2277; found: 305.2265.
Compound 2j: Enolsilane 2j was obtained from acrolein 1j (91 mg,
0.50 mmol) as a 1:50 mixture of Z/E isomers as a colourless oil (140 mg,
1
94%). H NMR (250 MHz, CDCl3): d=0.60–0.70 (m, 6H; 3ꢂCH2), 0.92–
1.01 (m, 9H; 3ꢂCH3), 1.25–1.51 (m, 6H; 3ꢂCH2), 1.84–1.93 (m, 2H;
CH2), 2.14–2.23 (m, 2H; CH2), 3.72 (s, 3H; CH3), 4.96 (dt, J=7.5,
11.8 Hz, 1H; CH), 5.80 (dt, J=1.5, 15.5 Hz, 1H; CH), 6.23 (dt, J=1.3,
12.0 Hz, 1H; CH), 6.95 ppm (dt, J=7.0, 15.8 Hz, 1H; CH); 13C NMR
(63 MHz, CDCl3): d=4.7, 6.7, 27.2, 27.5, 30.1, 32.2, 51.6, 111.2, 121.1,
140.4, 149.8, 167.4 ppm; IR (neat): 2953, 1726, 1658, 1164, 730 cmÀ1
;
HRMS (ESI+): m/z calcd for C16H30O3SiNa: 321.1862; found: 321.1850.
Compound 2c: Enolsilane 2c was obtained from acrolein 1c (56 mg,
0.50 mmol) as the Z isomer as a colourless oil (107 mg, 93%). 1H NMR
(250 MHz, CDCl3): d=0.60–0.69 (m, 6H; 3ꢂCH2), 0.95–1.01 (m, 9H; 3ꢂ
CH3), 1.13 (s, 9H; 3ꢂCH3), 1.47 (d, J=1.5 Hz, 3H; CH3), 5.98 ppm (d,
J=1.5 Hz, 1H; CH); 13C NMR (63 MHz, CDCl3): d=4.7, 6.9, 17.0, 29.5,
Compound 2k: Enolsilane 2k was obtained from acrolein 1k (110 mg,
0.50 mmol) as a 1:50 mixture of Z/E isomers as a colourless oil (146 mg,
1
87%). H NMR (250 MHz, CDCl3): d=0.61–0.71 (m, 6H; 3ꢂCH2), 0.95–
1.01 (m, 9H; 3ꢂCH3), 1.58–1.69 (m, 2H; CH2), 1.94–2.03 (m, 2H; CH2),
3.42–3.47 (m, 2H; CH2), 3.80 (s, 3H; CH3), 4.43 (s, 2H; CH2) 4.98 (dt,
J=7.5, 12.0 Hz, 1H; CH), 6.25 (dt, J=1.5, 11.8 Hz, 1H; CH), 6.86–6.90
63.8, 122.0, 133.6 ppm; IR (neat): 2955, 2877, 1650, 1160, 728 cmÀ1
;
HRMS (EI): m/z calcd for C13H28OSi: 228.1909; found: 228.1883.
Chem. Eur. J. 2011, 17, 8404 – 8413
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8409

P. M. Pihko et al.
(m, 2H; 2ꢂCH), 7.25–7.28 ppm (m, 2H; 2ꢂCH); 13C NMR (63 MHz,
CDCl3): d=4.6, 6.7, 14.3, 24.2, 30.7, 55.4, 69.6, 72.8, 111.0, 113.9, 129.4,
CDCl3): d=4.7, 6.8, 25.5, 27.2, 27.3, 28.7, 30.8, 122.0, 130.9 ppm; IR
(neat): 2927, 1679, 1152, 727 cmÀ1
;
HRMS (ESI+): m/z calcd for
131.0, 140.5, 159.3 ppm; IR (neat): 2954, 2876, 1512, 819, 729 cmÀ1
;
C13H26OSiNa: 226.1753; found: 226.1680.
HRMS (ESI+): m/z calcd for C19H32O3SiNa: 359.2018; found: 359.2013.
Compound 2s: Enolsilane 2s was obtained from enone 1s (35 mg,
0.50 mmol) as a 1:3 mixture of Z/E isomers as a colourless oil (88 mg,
95%). H NMR (250 MHz, CDCl3): d=0.63–0.73 (m, 6H; 3ꢂCH2), 0.95–
1.04 (m, 9H; 3ꢂCH3), 1.49–1.54 (m, 3H; CH3), [1.74 (m, 3H; CH3)],
1.79 (m, 3H; CH3), 4.45 (dq, J=0.8, 6.5 Hz, 1H; CH), [4.64–4.72 ppm
(dq, J=0.8, 6.5 Hz, 1H; CH)]; 13C NMR (63 MHz, CDCl3): d=5.5, 6.6,
10.5, 22.6, 102.2 ppm; IR (neat): 3293, 2954, 2877, 823, 724 cmÀ1; HRMS
(ESI+): m/z calcd for C10H23OSi: 187.1518; found: 187.1527.
Compound 2l: Enolsilane 2l was obtained from acrolein 1l (39 mg,
0.40 mmol) as a 1:12 mixture of Z/E isomers as a colourless oil (71 mg,
1
1
83%). H NMR (250 MHz, CDCl3): d=0.61–0.71 (m, 6H; 3ꢂCH2), 0.85–
0.91 (m, 3H; CH3), 0.95–1.01 (m, 9H; 3ꢂCH3), 1.27–1.32 (m, 4H; 2ꢂ
CH2), 1.84–1.92 (m, 2H; CH2), 4.99 (dd, J=7.5, 12.0 Hz, 2H; CH2),
6.23 ppm (d, J=12.0 Hz, 1H; CH); 13C NMR (63 MHz, CDCl3): d=4.7,
6.7, 14.1, 22.3, 27.2, 32.8, 111.9, 140.0 ppm; IR (neat): 2956, 2877, 1663,
1163, 728 cmÀ1; HRMS (ESI+): m/z calcd for C12H25OSi: 213.1674;
found: 213.1641.
Compound 2t: Enolsilane 2t was obtained from enone 1t (41 mg,
0.50 mmol) as
a
colourless oil (90 mg, 91%). 1H NMR (250 MHz,
Compound 2m: Enolsilane 2m was obtained from acrolein 1m (46 mg,
0.30 mmol) as the isomer E as a colourless oil (73 mg, 90%). 1H NMR
(250 MHz, CDCl3): d=0.62–0.68 (m, 6H; 3ꢂCH2), 0.96–1.02 (m, 9H; 3ꢂ
CH3), 1.21–1.35 (m, 4H; 2ꢂCH2), 1.60 (s, 3H; CH3), 1.69 (s, 3H; CH3),
1.89–2.06 (m, 3H; CH3), 4.86 (dd, J=8.8, 12.0 Hz, 1H; CH), 5.06–5.13
(m, 1H; CH), 6.21 ppm (d, J=12.0 Hz, 1H; CH); 13C NMR (63 MHz,
CDCl3): d=4.7, 6.8, 17.9, 22.2, 25.9, 26.2, 32.4, 38.1, 118.1, 125.0, 131.3,
139.2 ppm; IR (neat): 2956, 2913, 2877, 1660, 1239, 729 cmÀ1; HRMS
(ESI+): m/z calcd for C16H32OSiNa: 291.2120; found: 291.2119.
CDCl3): d=0.65–0.73 (m, 6H; 3ꢂCH2), 0.93–1.01 (m, 9H; 3ꢂCH3),
1.79–1.91 (m, 2H; CH2), 2.26 (t, J=7.3 Hz, 4H; 2ꢂCH2), 4.62 ppm (brs,
1H; CH); 13C NMR (63 MHz, CDCl3): d=5.0, 6.8, 21.7, 28.9, 33.7, 81.7,
102.3 ppm; IR (neat): 2956, 2913, 2877, 1660, 1457, 1414, 1377, 1239,
1159, 1005, 974, 922, 789, 729, 677 cmÀ1; HRMS (ES+): m/z calcd for
C11H22OSi: 198.1440; found: 198.1447.
General procedure for the preparation of aldehydes and ketones under
aqueous conditions: The acrolein (0.50 mmol, 100 mol%) and the tri-
AHCTUNGERTGeNNUN thylsilane (89 mL, 0.55 mmol, 110 mol%) were added to a suspension of
Compound 2n: Enolsilane 2n was obtained from acrolein 1n (102 mg,
0.50 mmol) as the isomer E as a colourless oil (152 mg, 95%). 1H NMR
(250 MHz, CDCl3): d=0.66–0.75 (m, 6H; 3ꢂCH2), 0.99–1.05 (m, 12H;
4ꢂCH3), 1.45–1.66 (m, 2H; CH2), 1.96–2.13 ( m, 1H; CH), 2.46–2.65 (m,
2H; CH2), 3.80 (s, 3H; CH3), 4.92 (dd, J=8.8, 12.0 Hz, 1H; CH), 6.26 (d,
J=12.0 Hz, 1H; CH), 6.84 (d, J=8.5 Hz, 2H; 2ꢂCH), 7.10 ppm (d, J=
8.5 Hz, 2H; 2ꢂCH); 13C NMR (63 MHz, CDCl3): d=4.7, 6.8, 22.3, 32.4,
33.0, 40.0, 55.4, 113.9, 117.8, 129.4, 135.2, 139.6, 157.8 ppm; IR (neat):
2951, 2912, 2870, 1661, 1456, 1410, 1375, 1238, 1157, 1009, 974, 918, 788,
725, 671 cmÀ1; HRMS (ES+): m/z calcd for C19H32O2Si: 320.2172; found:
320.2189.
PdCl2 (1.3 mg, 0.0075 mmol, 1.5 mol%) and PCy3 (4.2 mg, 0.015 mmol,
3.0 mol%) in a mixture THF/H2O (c(acrolein) =1.0m). The reaction mixture
was stirred at RT. After 5 min, the mixture became dark (black or
brown). The reaction could be followed by TLC (eluent: hexane/ethyl
acetate 9:1) or GC. After completion of the reaction (1 h on average),
the reaction mixture was filtered through a pad of alumina (2ꢂ2 cm) and
eluted with hexanes (2ꢂ10 mL). (Note that the aqueous layer was re-
tained by the alumina.) The filtrate was concentrated to around 1/10 of
the original volume and the residue was purified by flash chromatogra-
phy (silica gel, hexanes/diethyl ether 99:1) to afford the pure products.
Compound 3a: Saturated aldehyde 3a was obtained from acrolein 1a
(1.462 g, 10.0 mmol) as an oil (1.373 g, 93%). Rf =0.57 (hex); NMR data
corresponds to that published in the literature.[25] 1H NMR (250 MHz,
CDCl3): d=1.10 (d, J=7.0 Hz, 3H; CH3), 2.57–2.75 (m, 2H; CH2), 3.07–
3.14 (m, 1H; CH), 7.17–7.34 (m, 5H; 5ꢂCH), 9.72 ppm (d, J=1.5 Hz,
1H; CHO); 13C NMR (63 MHz, CDCl3): d=13.4, 36.8, 48.2, 126.6, 128.7,
129.2, 139.0, 204.4 ppm, HRMS (ESI+): m/z calcd for C10H12ONa:
171.0786; found: 171.0789.
Compound 2o: Enolsilane 2o was obtained from acrolein 1o (77 mg,
0.34 mmol) as a 1:10 mixture of Z/E isomers as a colourless oil (109 mg,
1
96%). H NMR (250 MHz, CDCl3): d=0.60–0.69 (m, 6H; 3ꢂCH2), 0.93–
1.00 (m, 9H; 3ꢂCH3), 1.16–1.32 (m, 2H; CH2), 1.44 (s, 9H; 3ꢂ CH3),
1.58–1.63 (m, 2H; CH2), 1.93–2.08 (m, 1H; CH), 2.66–2.77 (m, 2H;
CH2), 4.01–4.06 (m, 2H; CH2), 4.94 (dd, J=7.8, 12.0 Hz, 1H; CH),
6.27 ppm (dd, J=1.0, 12.0 Hz, 1H; CH); 13C NMR (63 MHz, CDCl3): d=
4.7, 6.7, 28.7, 33.15, 35.2, 44.0, 79.4, 116.2, 139.8, 155.1 ppm; IR (neat):
Compound 3b: Saturated aldehyde 3b was obtained from acrolein 1b
(50 mg, 0.30 mmol) as a mixture of diastereoisomers as a colourless oil
(42 mg, 84%). 1H NMR (1.5:1 mixture of diastereomers) (250 MHz,
CDCl3): d=0.96–1.04 (m, 6H; 2ꢂCH3), 1.23–1.27 (m, 2H; CH2), 1.59 (s,
3H; CH3), 1.67 (s, 3H; CH3), 1.85–2.07 (m, 3H; CH2 +CH), 2.22–2.38
(m, 1H; CH), 5.03–5.11 (m, 1H; CH), 9.65 ppm (dd, J=1.8, 7.0 Hz, 1H;
CHO); 13C NMR (63 MHz, CDCl3): d=8.3, 10.1, 14.3, 15.6, 17.5, 17.8,
22.8, 25.5, 25.9, 27.1, 31.8, 32.4, 33.5, 33.6, 34.9, 35.0, 50.7, 51.7, 124.2,
3433, 2915, 1692, 1365, 730 cmÀ1
; HRMS (ESI+): m/z calcd for
C18H35NO3SiNa: 364.2284; found: 364.2281.
Compound 2p: Enolsilane 2p was obtained from acrolein 1p (62 mg,
0.50 mmol) as a 1:10 mixture of Z/E isomers as a colourless oil (119 mg,
1
99%). H NMR (250 MHz, CDCl3): d=0.61–0.70 (m, 6H; 3ꢂCH2), 0.86–
0.91 (m, 2H; CH2), 0.98 (m, 9H; 3ꢂCH3), 1.26–1.27 (m, 2H; CH2), 1.63–
1.71 (m, 6H; 3ꢂCH2), 1.78–1.92 (m, 1H; CH), [4.31 (dd, J=6.0, 9.0 Hz,
1H; CH)], 4.97 (dd, J=8.0, 12.0 Hz, 1H; CH), [6.10 (dd, J=1.0, 6.0 Hz,
1H; CH)], 6.24 ppm (dd, J=0.8, 12.0 Hz, 1H; CH); 13C NMR (63 MHz,
CDCl3): d=4.7, 6.7, 26.4, 27.2, 34.4, 37.0, 118.5, 138.8 ppm; IR (neat):
2922, 1660, 1162, 729 cmÀ1; HRMS (ESI+): m/z calcd for C14H28O3SiNa:
263.1807; found: 263.1813.
124.3, 132.0, 205.7, 205.8 ppm; IR (neat): , 2927, 1726, 1456, 1379 cmÀ1
;
HRMS (ESI+): m/z calcd for C11H20ONa+CH3OH: 223.1674; found:
223.1675.
Compound 3 f: Saturated aldehyde 3 f was obtained from acrolein 1 f
(92 mg, 0.50 mmol) as a mixture of diastereoisomers as a colourless oil
(73 mg, 78%). 1H NMR (1.5:1 mixture of diastereomers) (250 MHz,
CDCl3): 0.84–0.91 (m, 6H; 2ꢂCH3), 1.21 (d, J=7.3 Hz, 3H; CH3), 1.56–
1.67 (m, 4H; 2ꢂCH2), 2.50–2.64 (m, 1H; CH), 3.57–3.67 (m, 2H; CH),
4.10–4.18 (m, 1H; CH), 4.21–4.31 (m, 1H; CH), 9.71 (d, J=0.5 Hz, 1H;
CHO), 9.78 ppm (d, J=2.0 Hz, 1H; CHO); 13C NMR (63 MHz, CDCl3):
d=8.1, 8.4, 10.2, 29.3, 29.5, 29.7, 29.9, 49.8, 68.2, 75.8, 113.0, 203.3 ppm;
IR (neat): 2941, 1710, 1460, 1057, 918, 730 cmÀ1; HRMS (ESI+): m/z
calcd for C10H18O3Na: 209.1154; found: 209.1151.
Compound 2q: Enolsilane 2q was obtained from acrolein 1q (75 mg,
0.30 mmol) as a 7:1 mixture of Z/E isomers as a colourless oil (90 mg,
1
82%). H NMR (250 MHz, CDCl3): d=0.74 (q, J=7.8 Hz, 6H; 3ꢂCH2),
1.05 (t, J=7.8 Hz, 9H; 3ꢂCH3), 1.63–1.76 (m, 2H; CH2), 1.90 (t, J=
7.5 Hz, 2H; CH2), 2.56 (t, J=7.5 Hz, 2H; CH2), 3.50 (s, 2H; CH2), [3.68
(s, 2H; CH2)], 6.27 (s, 1H; CH), [6.60 (s, 1H; CH)], 7.09–7.32 ppm (m,
10H; 10ꢂCH); 13C NMR (63 MHz, CDCl3): d=4.8, 6.8, 30.0, 30.9, 32.9,
35.6, 119.8, 125.7, 125.8, 128.3, 128.4, 128.6, 129.0, 135.3, 141.4,
142.9 ppm; IR (neat): 2955, 2876, 727, 696 cmÀ1; HRMS (ESI+): m/z
calcd for C24H34OSiNa: 389.2277; found: 389.2262.
Compound 3g: Saturated aldehyde 3g was obtained from acrolein 1g
(50 mg, 0.31 mmol) as a mixture of diastereoisomers as a colourless oil
(42 mg, 84%). 1H NMR (1:1 mixture of diastereoisomers) (250 MHz,
CDCl3): d=0.91 and 1.09 (2ꢂd, J=7.0 Hz, 2ꢂ3H; CH3), 1.31 (2ꢂd, J=
7.0 Hz, 2ꢂ3H; CH3), 2.29–2.69 (m, 2ꢂ1H; 2ꢂCH), 2.96–3.08 and 3.11–
3.22 (m, 2ꢂ1H; 2ꢂCH), 7.16–7.35 (m, 2ꢂ5H; 5ꢂCH), 9.60 (d, J=
2.0 Hz, 1H; CHO), 9.70 ppm (d, J=3.3 Hz, 1H; CHO); 13C NMR
Compound 2r: Enolsilane 2r was obtained from acrolein 1r (57 mL,
0.05 mmol) as a Colourless oil (100 mg, 88%). 1H NMR (250 MHz,
CDCl3): d=0.65 (q, J=8.0 Hz, 6H; 3ꢂCH2), 0.99 (t, J=8.0 Hz, 9H; 3ꢂ
CH3), 1.44–1.54 (m, 6H; 3ꢂCH2), 1.93 (t, J=5.0 Hz, 2H; CH2), 2.20 (t,
J=5.0 Hz, 2H; CH2), 6.05 ppm (s, 1H; CH); 13C NMR (63 MHz,
8410
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 8404 – 8413

Stereoselective Hydrosilylation of Enals and Enones
FULL PAPER
(63 MHz, CDCl3): d=10.7, 12.7, 17.7, 20.3, 40.4, 41.1, 52.7, 53.1, 126.8,
127.7, 127.8, 128.7, 204.9, 205.0 ppm, IR (neat): 2978, 1720, 1179,
701 cmÀ1; HRMS (ESI+): m/z calcd for C11H14O2Na: 201.0891; found:
201.0889.
CDCl3): d=0.88 (d, J=6.8 Hz, 3H; CH3), 2.00–2.16 (m, 1H; CH), 2.36
(dd, J=9.5, 13.5 Hz, 1H; CH(H)), 2.93 (dd, J=5.5, 15.8 Hz, 1H;
CH(H)), 3.40 (s, 3H; CH3), 3.41 (s, 3H; CH3), 4.08 (d, J=6.3 Hz, 1H;
CH), 7.17–7.33 ppm (m, 1H; 5ꢂCH); 13C NMR (63 MHz, CDCl3): d=
14.1, 38.0, 38.3, 54.3, 54.5, 108.5, 125.9, 128.4, 129.4, 140.8 ppm; IR (neat):
2932, 1058, 745, 699 cmÀ1; HRMS (ESI+): m/z calcd for C12H18O2Na:
217.1204; found: 217.1207.
Compound 3i: Saturated aldehyde 3i was obtained from acrolein 1i
(82 mg, 0.50 mmol) as a mixture of diastereoisomers as a colourless oil
(72 mg, 87%). 1H NMR (5:4 mixture of diastereomers) (250 MHz,
CDCl3): d=0.98 (d, J=7.0 Hz, 3H; CH3), 1.04 (d, J=7.0 Hz, 3H; CH3),
1.20 (d, J=7.3 Hz, 3H; CH3), 1.28 (d, J=7.3 Hz, 3H; CH3), 2.23 (d, J=
3.8 Hz, 3H; CH3), 2.53–2.77 (m, 1H; CH), 3.19–3.33 (m, 1H; CH), 5.84–
5.85 (m, 1H; CH), 5.90 (d, J=3.0 Hz, 1H; CH3), 9.70 ppm (dd, J=1.5,
7.3 Hz, 1H; CHO); 13C NMR (63 MHz, CDCl3): d=9.9, 10.6, 13.7, 14.3,
14.9, 16.6, 22.9, 31.8, 33.5, 34.3, 50.3, 51.1, 105.9, 106.0, 106.3, 106.6, 151.0,
151.1, 155.1, 155.6, 204.7, 204.9 ppm; IR (neat): 2973, 2957, 2851, 1375,
1078 cmÀ1; HRMS (ESI+): m/z calcd for C10H14O2Na: 189.0891; found:
189.0896.
Compound 4a’: Acetal 4a’ was obtained from acrolein 1a (73 mg,
0.50 mmol) as
a
colourless oil (89 mg, 93%). 1H NMR (250 MHz,
CDCl3): d=0.91 (d, J=6.8 Hz, 3H; CH3), 1.99–2.15 (m, 1H; CH), 2.42
(dd, J=9.8, 13.3 Hz, 1H; CH(H)), 2.96 (dd, J=5.0, 13.3 Hz, 1H;
CH(H)), 3.86–4.02 (m, 4H; 2ꢂCH2), 4.77 (d, J=4.0 Hz, 1H; CH), 7.18–
7.33 ppm (m, 1H; 5ꢂCH); 13C NMR (63 MHz, CDCl3): d=13.5, 37.9,
39.1, 65.3, 107.1, 126.0, 128.4, 129.4, 140.7 ppm; IR (neat): , 1067, 944,
744, 699 cmÀ1; HRMS (ESI+): m/z calcd for C12H16O2Na: 215.1048;
found: 215.1039.
Compound 3m: Saturated aldehyde 3m was obtained from acrolein 1m
(76 mg, 0.50 mmol) as a colourless oil (71 mg, 92%). The NMR data cor-
responds to that published in the literature.[26] 1H NMR (250 MHz,
CDCl3): d=0.97 (d, J=6.8 Hz, 3H; CH3), 1.23–1.44 (m, 2H; CH2), 1.60
(s, 3H; CH3), 1.68 (s, 3H; CH3), 1.95–2.04 (m, 2H; CH2), 2.05–2.13 (m,
1H; CH), 2.22 (ddd, J=2.5, 7.8, 15.8 Hz, 1H; CH(H)), 2.40 (ddd, J=2.0,
5.5, 15.8 Hz, 1H; CH(H)), 5.05–5.12 (m, 1H; CH), 9.75 ppm (t, J=
2.0 Hz, 1H; CHO); 13C NMR (63 MHz, CDCl3): d=17.9, 20.1, 25.6, 25.9,
28.0, 37.2, 51.2, 124.3, 131.9, 203.1 ppm, HRMS (ESI+): m/z calcd for
C10H18O2Na: 193.1204; found: 193.1200.
Compound 4 f: Acetal 4 f was obtained from acrolein 1 f (92 mg,
0.50 mmol) as a 2.5:1 mixture of diastereoisomers as a colourless oil
(94 mg, 81%). 1H NMR (2.5:1 mixture of diastereomers) (250 MHz,
CDCl3): 0.84–0.93 (m, 9H; 3ꢂCH3), 1.55–1.68 (m, 4H; 2ꢂCH2), 1.96–
2.09 (m, 1H; CH), 3.39 and 3.46 (2ꢂs, 6H; 2ꢂCH3), 3.51–3.64 (m, 1H;
CH), 3.94–4.05 (m, 1H; CH), [4.15 (d, J=6.8 Hz, 1H; CH), 4.34 ppm (d,
J=3.8 Hz, 1H; CH); 13C NMR (63 MHz, CDCl3): d=8.2, 8.5, 8.6, 29.8,
30.9, 40.2, 55.6, 56.8, 68.1, 107.1, 112.5 ppm; IR (neat): 2939, 1692, 1075,
732 cmÀ1; HRMS (ESI+): m/z calcd for C12H24O4Na: 255.1572; found:
255.1572.
Compound 3o: Saturated aldehyde 3o was obtained from acrolein 1o
(34 mg, 0.15 mmol) as a colourless oil (32 mg, 93%). The NMR data cor-
responds to that published in the literature.[27] 1H NMR (250 MHz,
CDCl3): d=1.07–1.26 (m, 2H; CH2), 1.43 (s, 9H; 3ꢂCH3), 1.64–1.69 (m,
2H; CH2), 1.94–2.12 (m, 1H; CH), 2.36 (dd, J=1.5, 6.8 Hz, 2H; CH2),
2.72 (dt, J=2.3, 13.3 Hz, 2H; CH2), 4.03–4.08 (m, 2H; CH2), 9.76 ppm (t,
J=1.5 Hz, 1H; CHO); 13C NMR (63 MHz, CDCl3): d=28.6, 30.9, 32.1,
43.9, 50.5, 79.6, 154.9, 201.6 ppm.
Compound 4h: Acetal 4h was obtained from acrolein 1h (70 mg,
0.50 mmol) as
CDCl3): d=0.87–0.90 (m, 6H; 2ꢂCH3), 3.34 (s, 6H; 2ꢂCH3), 4.01 ppm
(d, J=6.3 Hz, 1H; CH); 13C NMR (63 MHz, CDCl3): d=14.3, 14.5, 22.9,
27.1, 29.8, 31.9, 32.1, 35.9, 54.1, 54.3, 109.2 ppm; IR (neat): 2924, 1707,
a
colourless oil (87 mg, 93%). 1H NMR (250 MHz,
1465, 1110, 1057 cmÀ1
211.1674; found: 211.1672.
Compound 4o: Acetal 4o was obtained from acrolein 1o (34 mg,
0.15 mmol) as
colourless oil (39 mg, 95%). 1H NMR (250 MHz,
; HRMS (ESI+): m/z calcd for C11H24O2Na:
Compound 3q: Saturated aldehyde 3q was obtained from acrolein 1q
a
1
(75 mg, 0.30 mmol) as a colourless oil (66 mg, 87%). H NMR (250 MHz,
CDCl3): d=1.26 (m, 2H; CH2), 1.44 (s, 9H; 3ꢂCH3), 1.52–1.54 (m, 2H;
CH2), 1.64–1.69 (m, 2H; CH2), 2.68 (dt, J=2.5, 13.3 Hz, 2H; CH2), 3.30
(s, 6H; 2ꢂCH3), 4.02–4.08 (m, 2H; CH2), 4.46 ppm (t, J=5.5 Hz, 1H;
CH); 13C NMR (63 MHz, CDCl3): d=14.3, 22.9, 28.7, 31.8, 32.4, 32.5,
39.2, 44.1, 52.8, 79.4, 102.7, 155.1 ppm; IR (neat): 2931, 1688, 1419, 1163,
1122 cmÀ1; HRMS (ESI+): m/z calcd for C14H27NO4Na: 296.1838; found:
296.1827.
CDCl3): 1.52–1.61 (m, 2H; CH2), 1.64–1.79 (m, 2H; CH2), 2.55–2.69 (m,
4H; 2ꢂCH2), 2.72–2.82 (m, 1H; CH), 2.96–3.04 (m, 1H; CH), 7.14–7.36
(m, 10H; 10ꢂCH), 9.67 ppm (d, J=2.5 Hz, 1H; CHO); 13C NMR
(63 MHz, CDCl3): d=28.3, 28.9, 35.2, 36.0, 53.5, 126.1, 126.6, 128.6,
128.8, 129.2, 204.6 ppm; IR (neat): 2928, 1702, 696 cmÀ1; HRMS (ESI+):
m/z calcd for C18H20ONa: 275.1412; found: 275.1402.
Compound 3u: Saturated ketone 3u was obtained from enone 1u
(42 mg, 0.20 mmol), as a colourless oil (38 mg, 91%). The NMR data cor-
responds to that published in the literature.[28] 1H NMR (250 MHz,
CDCl3): d=3.08 (t, J=7.6 Hz, 2H; CH2), 2.38 ppm (t, J=7.6 Hz, 2H;
CH2); 13C NMR (63 MHz, CDCl3): d=14.2, 22.8, 24.0, 29.2, 29.3, 29.9,
31.8, 44.0, 209.4 ppm.
Compound 4r: Acetal 4r was obtained from acrolein 1r (55 mg,
0.50 mmol) as
a
colourless oil (70 mg, 89%). 1H NMR (250 MHz,
CDCl3): d=0.96–1.06 (m, 2H; CH2), 1.15–1.21 (m, 2H; CH2), 1.23–1.31
(m, 1H; CH), 1.52–1.67 (m, 2H; CH2), 1.70–1.79 (m, 4H; 2ꢂCH2), 3.33
(s, 6H; 2ꢂCH3), 3.98 ppm (d, J=7.0 Hz, 1H; CH); 13C NMR (63 MHz,
CDCl3): d=26.0, 26.6, 28.3, 40.3, 53.8, 108.8 ppm; IR (neat): 2954, 2927,
2877, 1716, 1679, 1458, 1448, 1414, 1379, 1237, 1213, 1152, 1089, 1068,
1004, 972, 818, 727, 685 cmÀ1; HRMS (ESI+): m/z calcd for C9H18O2Na:
181.1204; found: 181.1200.
Compound 3v: Saturated ketone 3v was obtained from enone 1v (83 mL,
0.50 mmol) as a colourless oil (67 mg, 94%). The NMR data corresponds
to that published in the literature.[29] 1H NMR (250 MHz, CDCl3): d=
0.82–0.87 (m, 3H; CH3), 1.24 (m, 8H; 4ꢂCH2), 1.48–1.60 (m, 2H; CH2),
2.10 (s, 3H; CH3), 2.38 ppm (t, J=7.5 Hz, 2H; CH2); 13C NMR (63 MHz,
CDCl3): d=14.2, 22.8, 24.0, 29.2, 29.3, 29.9, 31.8, 44.0, 209.4 ppm.
Compound 4v: Acetal 4v was obtained from acrolein 1v (83 mL,
0.50 mmol) as
a
colourless oil (87 mg, 94%). 1H NMR (250 MHz,
CDCl3): d=0.85 (m, 3H; CH3), 1.25–1.28 (m, 10H; 5ꢂCH2), 1.32–1.40
(m, 3H; CH3), 1.56–1.63(m, 2H; CH2), 3.87–3.92 ppm (m, 4H; 2ꢂCH2);
13C NMR (63 MHz, CDCl3): d=14.2, 22.8, 23.9, 24.3, 29.4, 30.0, 32.0,
39.4, 64.8, 110.4 ppm; IR (neat): 2945, 2866, 1718, 1445, 1369, 1339, 1278,
1111, 1056, 935, 825 cmÀ1; HRMS (ESI+): m/z calcd for C11H22O2H:
187.1698; found: 187.1710.
General procedure for the preparation of acetals: The acrolein
(0.50 mmol, 100 mol%) and the triethylsilane (89 mL, 0.55 mmol,
110 mol%) were added to a suspension of PdCl2 (1.3 mg, 0.0075 mmol,
1.5 mol%) and PCy3 (4.2 mg, 0.015 mmol, 3.0 mol%) in a mixture THF/
MeOH or THF/ethylene glycol (c(acrolein) =0.3m). The reaction mixture
was stirred at RT. After 5 min, the mixture became dark (black or
brown). The reaction could be followed by TLC (eluent: hexanes/ethyl
acetate 9:1) or GC. After completion of the reaction (1 h on average),
the reaction mixture was carefully concentrated and the residue was puri-
fied by flash chromatography (silica gel, hexanes/diethyl ether 99:1) to
afford the pure products.
Compound 4w: Acetal 4w was obtained from enone 1w (48 mL,
0.50 mmol) as
a
colourless oil (70 mg, 98%). 1H NMR (250 MHz,
CDCl3): d=1.39–1.42 (m, 2H; CH2), 1.60 (t, J=2.8 Hz, 8H; 4ꢂCH2),
3.93 ppm (s, 4H; 2ꢂCH2); 13C NMR (63 MHz, CDCl3): d=24.2, 25.4,
35.4, 64.4, 109.3 ppm; IR (neat): 2933, 2862, 1099, 1037, 924 cmÀ1; HRMS
(ESI+): m/z calcd for C8H15O2: 143.1072; found: 143.1069.
Compound 4a: Acetal 4a was obtained from acrolein 1a (30 mg,
0.20 mmol) as
Recycling of the catalyst: Acrolein 1a (44 mg, 0.30 mmol, 100 mol%),
the triethylsilane (53 mL, 0.33 mmol, 110 mol%) and the internal stan-
a
colourless oil (37 mg, 95%). 1H NMR (250 MHz,
Chem. Eur. J. 2011, 17, 8404 – 8413
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8411

P. M. Pihko et al.
dard dibenzyl ether (11 mL, 0.06 mmol, 20 mol%) were added to a sus-
pension of PdCl2 (1.6 mg, 0.009 mmol, 3.0 mol%) and PCy3 (5.0 mg,
0.018 mmol, 6.0 mol%) in dry THF (1.0 mL, c(acrolein) =0.3m). The reac-
tion was followed by GC. After full conversion was observed the reaction
mixture was centrifuged 5 min (5200 rpm). The solution phase was re-
moved and the solid material was rinsed with THF (1.0 mL) and centri-
fuged 2 min (5200 rpm). Rinsing was repeated twice. The solid material
was mixed with THF (1.0 mL) and the acrolein 1a (44 mg, 0.30 mmol,
100 mol%), the triethylsilane (53 mL, 0.33 mmol, 110 mol%) and the in-
ternal standard dibenzyl ether (11 mL, 0.06 mmol, 20 mol%) were added
to the suspension. The reaction was followed by GC. After full conver-
sion of 1a, the recycling procedure was repeated.
Tekes (Enabling Synthesis Technologies platform) and by the University
of Jyvꢀskylꢀ, Department of Chemistry.
[1] a) J. Durand, E. Teuma, M. Gꢃmez, Eur. J. Inorg. Chem. 2008,
3577–3586; b) R. G. Freemantle, M. Liu, W. Guo, S. O. Obare in
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[2] For examples of enantioselective processes catalysed by functional-
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Chem. 2009, 7, 2669–2677, and references therein; b) K. V. S. Ran-
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3982–3985.
[3] In the following enantioselective reactions, only a single substrate
was used: Pd-catalysed hydrosilylation: a) M. Tamura, H. Fujihara,
J. Am. Chem. Soc. 2003, 125, 15742–15743; Pd-catalysed allylic alky-
lation: b) S. Jansat, M. Gomez, K. Philippot, G. Muller, E. Guiu, C.
Claver, S. Castillon, B. Chaudret, J. Am. Chem. Soc. 2004, 126,
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2008, 350, 2583–2598; b) M. B. Thathagar, J. E. ten Elshof, G. Roth-
enberg, Angew. Chem. 2006, 118, 2952–2956; Angew. Chem. Int. Ed.
2006, 45, 2886–2890.
[5] For general reviews of conjugate reduction, see: a) P. A. Mayes, P.
Perlmutter in Modern Reduction Methods (Eds.: P. G. Andersson,
I. J. Munslow), Wiley-VCH, Weinheim, 2008, pp. 87–106; b) E.
Keinan, N. Greenspoon in Comprehensive Organic Synthesis (Eds.:
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557.
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catalysis, see: b) W. S. Mahoney, D. M. Brestensky, J. M. Stryker, J.
Am. Chem. Soc. 1988, 110, 291–293; for enantioselective conjugate
reduction: c) D. H. Appella, Y. Moritani, R. Shintani, E. M. Ferre-
ira, S. L. Buchwald, J. Am. Chem. Soc. 1999, 121, 9473–9474; d) G.
Hughes, M. Kimura, S. L. Buchwald, J. Am. Chem. Soc. 2003, 125,
11253–11258.
[7] a) E. Keinan, N. Greenspoon, J. Am. Chem. Soc. 1986, 108, 7314–
7325; for an enantioselective conjugate reduction, see: b) Y. Tsu-
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c) D. Monguchi, C. Beemelmanns, D. Hashizume, Y. Hamashima,
M. Sodeoka, J. Organomet. Chem. 2008, 693, 867–873.
[8] a) I. Ojima, T. Kogure, Y. Nagai, Tetrahedron Lett. 1972, 13, 5035–
5038; b) D. A. Evans, G. C. Fu, J. Org. Chem. 1990, 55, 5678–5680;
for an enantioselective conjugate reduction: c) Y. Kanazawa, H.
Nishiyama, Synlett 2006, 3343–3345.
Catalytic activity of the supernatant: According to our general procedure,
the PdNP catalyst suspension was prepared as follows: A suspension of
PdCl2 (1.6 mg, 0.009 mmol, 3.0 mol%) and PCy3 (5.0 mg, 0.018 mmol,
6.0 mol%) in dry THF (1.0 mL, c(acrolein) =0.3m) was stirred for 5 min and
Et3SiH (1.0 mL, 0.0063 mmol, 2,1%) was added to the mixture. After stir-
ring for another 5 min, the mixture was centrifuged for 5 min (5200 rpm).
The solution phase was separated by filtration through a 0.2 mm filter and
the acrolein 1a (44 mg, 0.30 mmol, 100 mol%), the triethylsilane (53 mL,
0.33 mmol, 110 mol%) and the internal standard: dibenzyl ether (11 mL,
0.06 mmol, 20 mol%) were added to the supernatant solution. The reac-
tion was followed by GC and after 12 h only the acrolein and the internal
standard were observed.
A sample of the supernatant was diluted with 65% HNO3 (1:10 dilution)
and subjected to inductively coupled plasma atomic emission spectrosco-
py (ICP-AES) analysis. The concentration of palladium in the superna-
tant was determined by three independent measurements, affording a
concentration of 35 mgLÀ1
.
Competition experiments: Et3SiD/Ph3SiH: Acrolein 1a (50 mg,
0.34 mmol, 100 mol%) and a mixture of deuterated triethylsilane (55 mL,
0.34 mmol, 100 mol%) and triphenylsilane (89 mg, 0.34 mmol,
100 mol%) in dry THF (0.1 mL) were added to a suspension of Pd-
ACHTUNGTRENNUNG(OAc)2 (0.9 mg, 0.005 mmol, 1.5 mol%) or PdCl2 (0.9 mg, 0.005 mmol,
1.5 mol%) and PCy3 (2.8 mg, 0.010 mmol, 3.0 mol%) in dry THF
(1.0 mL, c(acrolein) =0.3m). The reaction mixture was stirred at RT for 3 h.
The material was filtered through a pad of alumina, eluted with hexane
and concentrated in vacuo. The residue was purified by flash chromatog-
raphy (silica gel, hexanes or hexanes/diethyl ether 99:1) to afford the
pure products 2a and 2a’. 1H NMR spectroscopic analysis (250 MHz,
CDCl3) indicated that the CH3 signal at d=1.5 ppm had reduced in in-
tensity by 0.5H (see the Supporting Information).
No hydrolysis of the enolsilane 2a under aqueous conditions: Acrolein
1a (44 mg, 0.30 mmol, 100 mol%) and the triethylsilane (53 mL,
0.33 mmol, 110 mol%) were added to a suspension of PdCl2 (0.8 mg,
0.0045 mmol, 1.5 mol%) and PCy3 (2.5 mg, 0.009 mmol, 3.0 mol%) in a
mixture THF/H2O (c(acrolein) =1.0m). The reaction mixture was stirred at
RT. The reaction was monitored by GC (aliquot of reaction mixture di-
luted in CH2Cl2) or by 1H NMR spectroscopy (reaction in an NMR tube
using [D8]THF/H2O 10:1) and no enolsilane was formed, only acrolein
(starting material) and saturated aldehyde (final product) were observed.
When enolsilane 2a (66 mg, 0.25 mmol, 100 mol%) was added to a reac-
tion mixture containing acrolein 1a (37 mg, 0.25 mmol, 100 mol), PdCl2
(0.7 mg, 0.004 mmol, 1.5 mol%), PCy3 (2.1 mg, 0.0075 mmol, 3.0 mol%)
and Et3SiH (45 mL, 0.28 mmol, 110 mol%) in dry THF (0.8 mL, c(acrolein)
=
[9] Iron: a) J. P. Collman, R. G. Finke, P. L. Matlock, R. Wahren, R. G.
Komoto, J. I. Brauman, J. Am. Chem. Soc. 1978, 100, 1119–1140;
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2580; Tin: c) D. S. Hays, M. Scholl, G. C. Fu, J. Org. Chem. 1996, 61,
6751–6752; manganese: d) P. Magnus, M. J. Waring, D. A. Scott, Tet-
rahedron Lett. 2000, 41, 9731–9733; titanium: e) A. D. Kosal, B. L.
Ashfeld, Org. Lett. 2010, 12, 44–47.
0.3m) and stirred at RT overnight, no degradation of the enolsilane was
observed (as determined by GC by using dibenzyl ether as the internal
standard).
Acknowledgements
[10] a) L. H. Sommer, J. E. Lyons, J. Am. Chem. Soc. 1969, 91, 7061–
7067; b) M.-K. Chung, G. Orlova, J. D. Goddard, M. Schlaf, R.
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[11] a) M. Benohoud, A. Erkkilꢀ, P. M. Pihko, Org. Synth. 2010, 87, 201–
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[12] A. D. Petrov, S. J. Sadykh-Zade, Dokl. Akad. Nauk. SSSR 1958, 119.
We thank Hilkka Reunanen and Paavo Niuttanen for their assistance
during TEM measurements, Ari Vꢀisꢀnen for the ICP-AES analysis, and
Reijo Kauppinen for NMR spectroscopy and Mirja Lahtiperꢀ for mass
spectrometric assistance. We also thank Prof. Robert Whetten (Georgia
Tech, USA) for constructive comments. This work was supported by
8412
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 8404 – 8413

Stereoselective Hydrosilylation of Enals and Enones
FULL PAPER
[13] Y. Sumida, H. Yorimitsu, K. Oshima, J. Org. Chem. 2009, 74, 7986–
7989.
reaction mixture and subsequent hydrosilylation, afforded the a-me-
thylated product 3a in 95% overall yield.
[14] Details are provided in the Supporting Information.
[15] The only exception to the good chemoselectivity with aldehydes was
observed with cinnamaldehyde derivatives, for which the product of
1,2- hydrosilylation was obtained as the major product, even in pres-
ence of an electron-withdrawing group, such as the nitro group.
[23] The pH of the aqueous reaction mixture drops below two during the
course of the reaction (see the Supporting Information).
[24] Both O- and C-bound Pd enolates have been characterised in the
literature (for examples, see: D. A. Culkin, J. F. Hartwig, Organome-
tallics 2004, 23, 3398–3416). In a C-bound enolate, the selectivity
[16] The Oshima mechanism implies the formation of an oxapalladacycle
that would result in the formation of the E isomer instead of the ob-
served Z isomer.[13]
[17] B. P. S. Chauhan, J. S. Rathore, T. Bandoo, J. Am. Chem. Soc. 2004,
126, 8493–8500.
[18] a) Y. Lin, R. G. Finke, Inorg. Chem. 1994, 33, 4891–4910; b) C. M.
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[20] T. Teranishi, M. Miyake, Chem. Mater. 1998, 10, 594–600.
[21] In addition to PdCl2 as the catalyst precursor, preliminary experi-
ments indicated that Pd(OH)2/C (Pearlman catalyst) also displayed
hydrosilylation activity when treated with Et3SiH (full conversion in
3 h; 2a/3a ratio of 83:17).
[22] We also briefly examined the possibility of combining the a-meth-
ylenation process and the subsequent hydrosilylation process into a
one-pot aldehyde a-methylation procedure. For example, a-methyle-
nation of 3-phenylpropionaldehyde, followed by acidification of the
À
might be compromised by free rotation of around the C CHO
bond, and as such, we suggest that the O-bound Pd enolate is
formed. Importantly, this mechanism requires, for geometric reasons,
that hydride delivery and binding of the enolate to palladium take
place at different Pd atoms. This can be readily achieved by PdNPs,
but is difficult to achieve in solution with mononuclear Pd species.
[25] K. Maruoka, T. Itoh, M. Sakurai, K. Nonoshita, H. Yamamoto, J.
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[26] D. Savoia, E. Tagliavini, C. Trombini, A. Umani-Ronchi, J. Org.
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209–213.
Received: March 1, 2011
Published online: June 10, 2011
Chem. Eur. J. 2011, 17, 8404 – 8413
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8413