Palladium-catalyzed allylation reaction of alkynylborates

Article abstract of DOI:10.1246/bcsj.20100189

Alkynyl(aryl)(diorganyl)borates, anionic tetrahedral boron compounds, reacted with allylic bromides in the presence of a palladium(0) catalyst to produce (diorganyl)(trisubstituted alkenyl)boranes. Allylation took place at the alkynyl carbon β to boron, i

Full text of DOI:10.1246/bcsj.20100189

1380 Bull. Chem. Soc. Jpn. Vol. 83, No. 11, 1380–1385 (2010)
© 2010 The Chemical Society of Japan
Palladium-Catalyzed Allylation Reaction of Alkynylborates
Naoki Ishida, Tatsuo Shinmoto, Shota Sawano, Tomoya Miura, and Masahiro Murakami*
Department of Synthetic Chemistry and Biological Chemistry, Kyoto University, Katsura, Kyoto 615-8510
Received July 8, 2010; E-mail: murakami@sbchem.kyoto-u.ac.jp
Alkynyl(aryl)(diorganyl)borates, anionic tetrahedral boron compounds, reacted with allylic bromides in the presence
of a palladium(0) catalyst to produce (diorganyl)(trisubstituted alkenyl)boranes. Allylation took place at the alkynyl
carbon ¢ to boron, inducing 1,2-migration of the aryl group on the anionic boron center to the ¡-carbon.
Organoboron compounds have received ever-increasing
attention because of their interesting photophysical properties1
as well as facile reactivities as synthetic reagents. In particular,
organoboranes having ³-conjugation extended through a
vacant p-orbital on boron2 are attractive in terms of optoelec-
tronic materials such as light-emitting diodes,3 fluorescent
sensors,4 nonlinear optics,5 and two-photon emitters.6 There-
fore, organic skeletons containing alkenyl-boron linkages have
become a synthetic target of current interest. Among the most
conventional methods for the synthesis of alkenylboranes are
hydroboration reactions of alkynes and substitution reactions
of halo- and alkoxyboranes with alkenylmetal reagents.7 An
alternative pathway is available starting from alkynyltriorga-
nylborates,8 which react with a variety of electrophiles such
as a proton,9 organic halides,10 carbon dioxide,11 oxiranes,12
chlorophosphines,13 sulfenyl chlorides,14 metal halides,15 and
³-allylpalladium.16 An electrophile attacks the alkynyl carbon
¢ to boron, inducing 1,2-migration of an organyl group from
boron to the ¡-carbon. This class of reactions has provided a
valuable method to prepare trisubstituted alkenylboranes,
which are difficult to synthesize by the other conventional
methods mentioned above. For example, a reaction of hexyn-1-
yltrihexylborate with allyl bromide affords a 1,4-dienylborane
(eq 1). Allyl and hexyl groups are vicinally installed across the
boron-substituted carbon-carbon double bond.10b
have been limited to alkyl and alkenyl groups in the previous
cases. Herein, we describe our study on the palladium-catalyzed
reaction of alkynylborates with allylating reagents, in which an
aryl group on boron migrates onto the ¡-carbon.
Results and Discussion
Optimization of Reaction Conditions.
We initially
examined a non-catalyzed reaction of alkynyltriphenylborate
1a with allyl bromide. Alkynyltriphenylborate 1a was treated
with allyl bromide in toluene at 70 °C, and after 15 min, the
reaction was quenched by addition of acetic acid (eq 2). Only
protonated alkene 3a was obtained (87% yield), suggesting that
allyl bromide was not electrophilic enough to form a carbon-
carbon bond with alkynyltriphenylborate 1a. Instead, the proton
of acetic acid employed for quenching acted as the electrophile
toward 1a to promote the 1,2-migration of the phenyl group
from boron to the ¡-carbon.9 Further protodeborylation of the
resulting alkenylborane 2a afforded alkene 3a. Thus, alkynyl-
triarylborates were less reactive than alkynyltrialkylborates in
the non-catalyzed reaction with allyl bromide.10b
Br
1a (remained)
+
BPh3]
[Me4N][Ph(CH2)2
toluene, 70 °C
BPh2
Ph
1a
H
H
H
AcOH
AcOH
ð2Þ
Ph
Ph
Ph
2a
3a
87%
B(nC6H13 2
)
E Z = 7/93
/
Li[nBu
B(nC6H13)3]
Br
+
ð1Þ
nBu
nC6H13
Next, various palladium catalysts were examined in the
allylation reaction of alkynyltriarylborate 1a (Table 1). The
reaction mixture was quenched with acetic acid to obtain a
protodeborylated compound. When [Pd(PPh3)4], the active
catalyst for the reaction of alkynyltrialkylborates with allyl
carbonates,16a was employed, 1,4-diene 5a was obtained in
only 11% yield (Entry 1). The use of a palladium catalyst
modified with P(o-tol)3, which was a suitable catalyst for the
reaction with aryl halides,17 resulted in the formation of a
complex mixture (Entry 2). No desired product was observed
with DPPE and DPPF (Entries 3 and 4), whereas BINAP
afforded 5a in 42% yield (E/Z = 29/71, Entry 5). The
bidentate phosphine ligand XANTPHOS, possessing a rigid
and planar skeleton with a large bite angle of 108°,19 furnished
5a in 91% yield as a mixture of geometric isomers (E/Z =
We have recently developed a palladium-catalyzed reaction
of alkynyl(aryl)borates with aryl halides, which furnishes
trisubstituted alkenylboranes in a stereo-defined form.17
A
related reaction of alkynyltriarylborates having a tertiary
ammonium moiety produced azaboracycles having a boron-
nitrogen intramolecular coordination bond.18 In both reactions,
an aryl group on boron migrated to the ¡-sp2-carbon of the
produced alkenylborane. As a continuation of our investigation
on palladium-catalyzed reactions of alkynyltriarylborates, we
next examined the use of allyl halides as electrophiles. Although
palladium-catalyzed as well as non-catalyzed reactions of
alkynyltriorganylborates with allyl acetates, carbonates, and
halides have been reported,10b,16 the migrating organyl groups
Published on the web October 30, 2010; doi:10.1246/bcsj.20100189

N. Ishida et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 11 (2010) 1381
Table 1. Catalyst Screeninga)
D
91%
(b)
E
/Z = 54/46
BPh2
Ph
H
Ph
E
: 72%D, Z: 71%D
Pd catalyst
Br
AcOH
Ph
Ph
+
1a
5a-d
Ph
toluene, 70 °C
Ph
Ph
5a
4a
O
(a)
(c)
79%
Yield of
5a/%c)
1a
4a
Entry Catalystb) (mol %)
E/Zc)
Ph
6
1
2
[Pd(PPh3)4] (5)
11
complex
mixture
<1
72/28
OMe
[Pd2dba3]¢CHCl3 (2.5)/P(o-tol)3 (6)
®
(d)
50%
/Z = 44/56
3
4
5
6
7
[Pd2dba3]¢CHCl3 (2.5)/DPPE (6)
[Pd2dba3]¢CHCl3 (2.5)/DPPF (6)
[Pd2dba3]¢CHCl3 (2.5)/BINAP (6)
®
®
E
2
42
Ph
Ph
29/71
7
[Pd2dba3]¢CHCl3 (2.5)/XANTPHOS (6) 91 (91)d) 54/46
Scheme 1. Transformation of alkenylborane 4a. Reaction
conditions: (a) 2.5 mol % [Pd2dba3]¢CHCl3, 6 mol %
P(o-tol)3, 1.2 equiv allyl bromide, toluene, rt, 3 h. (b)
AcOD, rt, 3 h. (c) 5 equiv Me3NO, rt, 3 h. (d) 3.3 equiv
4-MeOC6H4Br, 9.0 equiv NaOH, H2O, rt, 10 h.
[Pd2dba3]¢CHCl3 (2.5)/DPEPHOS (6)
6
27/73
a) Reaction conditions: 1.0 equiv of 1a, 1.2 equiv of allyl
bromide, 5 mol % Pd catalyst, toluene, 70 °C, 15 min; then
AcOH, rt, 3 h. b) dba: dibenzylideneacetone. c) Determined by
GC analysis. d) Isolated yield.
5a
Table 2. Examination on Allylating Reagentsa)
93%
E
/
Z
= 50/50
1a
2.5 mol% [Pd2dba3]·CHCl3
(a)
6 mol% XANTPHOS
AcOH
+
+
X
5a
+
1a
[Me4N][nC5H11
B(C6H4-4-OMe)3]
toluene, 70 °C
H
1b
Entry
X
Yield of 5a/%b)
E/Zb)
nC5H11
1
2
3
Cl
OAc
OC(O)OMe
48
13
3
43/57
56/44
52/48
OMe
5b
88%
E/Z = 52/48
a) Reaction conditions: 1.0 equiv of 1a, 1.2 equiv of allylating
reagent, 2.5 mol % [Pd2dba3]¢CHCl3, 6 mol % XANTPHOS,
toluene, 70 °C, 15 min; then AcOH, rt, 3 h. b) Determined by
GC analysis.
Scheme 2. Crossover experiment. Reaction conditions:
(a) 5 mol % [Pd2dba3]¢CHCl3, 12 mol % XANTPHOS,
70 °C, 2.4 equiv allyl bromide, 15 min; then AcOH, rt, 3 h.
54/46, Entry 6). DPEPHOS, which also has a large bite angle
(104°) but is more flexible than XANTPHOS, provided the
product in only 6% yield (Entry 7).
Br
Allylating reagents other than allyl bromide were examined
(Table 2). Allyl chloride reacted with 1a under the same
reaction conditions, giving allylated product 5a in 48% yield
(Entry 1). Allyl acetate and allyl methyl carbonate were far less
reactive, affording only a small amount of the product 5a
(Entries 2 and 3). Thus, allylic bromides were used as the
allylating reagent in the following experiments.
Br
Pd
P
P
P
P
Pd
Mechanism. The following experiments were carried out
in order to prove the putative formation of the intermediate
alkenylborane 4a (Scheme 1). When AcOD was employed
instead of AcOH for quenching by protonolysis, deuterated
alkene 5a-d was isolated in 91% yield (E/Z = 54/46, 72%
incorporation of D for the E-isomer, 71% incorporation of D
for the Z-isomer). On the other hand, treatment of the reaction
mixture with trimethylamine N-oxide (5 equiv) instead of
acetic acid caused oxidation of the carbon-boron bond to afford
the ketone 6 in 79% yield. Furthermore, direct addition of p-
anisyl bromide and NaOH to the solution after the allylation
reaction provided the cross-coupling product 7 in 50% yield.
Thus, palladium-catalyzed allylation reaction of alkynylborates
1a resulted in the formation of alkenylborane 4a.
1a
4a + [Me4N]Br
Scheme 3. Plausible catalytic cycle.
Next, a crossover experiment was carried out (Scheme 2).
When a mixture of 1a (1.0 equiv) and 1b (1.0 equiv) was
subjected to the palladium-catalyzed reaction with allyl
bromide (2.4 equiv), 5a and 5b were obtained in 93 and 88%
yields, respectively. No crossover products were detected in the
1
reaction mixture by H NMR and GC-MS analysis, suggesting
that 1,2-aryl migration occurred in an intramolecular fashion.
A plausible catalytic cycle is depicted in Scheme 3. Initially,
allyl bromide oxidatively adds to palladium(0) to yield a
³-allylpalladium species ligated by the bidentate ligand

1382 Bull. Chem. Soc. Jpn. Vol. 83, No. 11 (2010)
Pd-Catalyzed Allylation of Alkynylborates
Table 3. Allylation of Various Alkynyltriarylboratesa)
a) syn
b) anti
2.5 mol% [Pd2dba3]·CHCl3
6 mol% XANTPHOS
AcOH
Br
+
BAr3]
[Me4N][R
toluene, 70 °C
R
Ar
P
P
P
P
1
Pd
5
Pd
Yield
/%b)
Entry Alkynyltriarylborate
R
Ar
E/Zc)
Ph
Ph
Ph
nC5H11 Ph
91
89
72
24
54/46
55/45
57/43
50/50
47/53
48/52
53/47
71/29
nC5H11
B
nC5H11
B
1
2
3
4
5
6
7d)
8
1c
1d
1e
1f
1g
1h
1i
Ph
Ph
iBu
iPr
Ph
Ph
Ph
Ph
Ph
Figure 1. Stereochemical courses of 1,2-migration of the
phenyl group on boron.
nC5H11 4-MeC6H4 89
nC5H11 3-MeC6H4 91
nC5H11 4-FC6H4
83
79
XANTPHOS. The alkynyl moiety of the borate nucleophili-
cally attacks the ³-allylpalladium species, inducing the 1,2-
phenyl migration from boron to the ¡-carbon (vide infra). The
alkenylborane 4a is formed and palladium(0) is regenerated
with release of a bromide anion.
1j
nC5H11 2-thienyl
a) Reaction conditions: 1.0 equiv of 1, 1.2 equiv of allyl
bromide, 2.5 mol % [Pd2dba3]¢CHCl3, 6 mol % XANTPHOS,
toluene, 70 °C, 15 min; then AcOH, rt, 3 h. b) Isolated yield.
c) Determined by 1H NMR analysis. d) Reaction time: 30 min.
No E/Z selectivity was observed with the allylation
products. This stereochemical outcome stands in marked
contrast to the high stereoselectivity observed in the arylation
reaction.17 Thus, it is inferred that a mechanism different from
the previous one is operating in the present reaction. We
assume the contrast observed in the stereoselectivities is
attributed to the structural difference between ³-allylpalla-
dium complex ligated by the bidentate phosphine ligand
XANTPHOS and ·-arylpalladium complex ligated by the
monodentate phosphine ligand P(o-tol)3. Tetracoordinated
[Pd(³-allyl)(xantphos)]+, which would be generated by oxida-
tive addition of allyl bromide, is sterically congested around
the palladium center, disfavoring additional direct ³-coordina-
tion of the alkynyl group to palladium. Instead, the other side
of the allyl ligand opposite to palladium is exposed enough to
be intermolecularly attacked by the alkynyl group of the borate.
Carbon-carbon bond formation between the allyl group and the
¢-carbon of the alkynylborate thus takes place at the opposite
side of palladium.20 Another carbon-carbon bond is concom-
itantly formed by 1,2-phenyl migration (Figure 1). It can
proceed in both syn- and anti-periplanar relationships to ³-
allylpalladium, giving a mixture of the stereoisomers. On the
other hand, tricoordinated [(o-tol)3P][Pd(aryl)Br], which is gen-
erated by oxidative addition of an aryl halide to palladium(0),
has a vacant site on palladium, allowing the alkynylborate
to coordinate.21 Consequently, it undergoes carbopalladation
across the carbon-carbon triple bond in a syn fashion, leading
to the stereoselective formation of the arylation product.
Reaction Scope. Various alkynylborates were subjected to
the palladium-catalyzed allylation reaction under the optimized
conditions (alkynyltriarylborate 1 (1.0 equiv), allyl bromide
(1.2 equiv), [Pd2dba3]¢CHCl3 (2.5 mol %), XANTPHOS (6
mol %), toluene, 70 °C, 15 min; then AcOH, rt, 3 h). The results
are summarized in Table 3. Alkynylborates with a primary
alkyl substituent yielded the corresponding 1,4-dienes in high
yield (Entries 1 and 2). In the case of a secondary alkyl
substituent, the yield was moderate (72%, Entry 3). Triphen-
yl(phenylethynyl)borate (1f) was less reactive and the yield
decreased to 24% (Entry 4). As the aryl group on boron, both
electron-donating and -accepting aryl groups could participate
in the reaction (Entries 5-7 and Scheme 2). The reaction of
alkynyltriarylborate 1i (Ar = 4-fluorophenyl) was slower than
those of 1c and 1g, requiring 30 min to complete (Entry 7). A
2-thienyl group also migrated to give the corresponding
product in 79% yield (Entry 8).
The allylation reaction of tert-butyl-substituted alkynyl-
borate 1k afforded 1-boryl-1,4-diene 4k in 28% yield (E/Z =
>95/5) and 1,4-diene 5k in 25% yield (E/Z = 18/82) after
quenching with acetic acid (eq 3). It was likely that a mixture
of (E)- and (Z)-isomers of 4k was formed initially. The boron-
carbon bond of the (E)-isomer was less labile to protodeboryl-
ation with acetic acid owing to the steric protection by the
neighboring tert-butyl group, which allowed partial isolation of
(E)-4k. The other isomer (Z)-4k together with some portion of
(E)-4k underwent protodeborylation to afford a mixture of 1,4-
diene 5k with the (Z)-isomer predominating. The reaction of
alkynylborate 1l equipped with a methoxymethyl substituent
gave a mixture of (E)-alkenylborane 4l (48% yield) and (Z)-
alkene 5l (38% yield) after addition of acetic acid (eq 4). The
(E)-alkenylborane 4l was stabilized by the intramolecular
coordination of the oxygen atom to remain as such, whereas the
other (Z)-isomer initially formed was facilely protodeborylated
to 5l. The coordination of oxygen to the boron center in (E)-4l
was supported by up-field shift of the 11B NMR signal (¤ 18.5).
2.5 mol% [Pd2dba3]·CHCl3
6 mol% XANTPHOS
AcOH
[Me4N][tBu
BPh3]
Br
+
ð3Þ
toluene, 70 °C
1k
Ph
+
H
tBu
BPh2
tBu
Ph
4k
28%
= >95/5
5k
25%
E/
Z
E/Z
= 18/82
2.5 mol% [Pd2dba3]·CHCl3
6 mol% XANTPHOS
AcOH
H
Br
[Me4N][MeOCH2
1l
BPh ]
+
3
ð4Þ
toluene, 70 °C
Ph
+
BPh2
Ph
O
OMe
Me
4l
5l
48%
38%
E
/Z
= >95/5
E
/Z
= <5/95

N. Ishida et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 11 (2010) 1383
We also conducted the allylation reaction with substituted
allylic bromides. The reaction of 1c with cinnamyl bromide
afforded the 1,4-diene 8 in 93% yield (E/Z = 42/58, eq 5).
A prenyl group was also incorporated into the product to
give 9 in 71% yield (E/Z = 53/47, eq 6). In both cases, a
carbon-carbon bond was formed at the less-substituted allylic
position.
SiMe3
iBu
5 mol%
Ph
[Pd(π-allyl)Cl(xantphos)]
B
[Me4N]
Br
+
toluene, rt
1n
Ph
B
iBu
Ph
SiMe3
SiMe3
B
+
ð8Þ
iBu
Ph
4n
38%
E/Z = <5/95
2.5 mol% [Pd2dba3]·CHCl3
H
10
28%
6 mol% XANTPHOS
AcOH
Ph
Br
+
1c
ð5Þ
nC5H11 Ph
toluene, 70 °C
8
Then, we tried to synthesize air-stable (¡-arylalkenyl)di-
arylboranes by increasing the steric bulkiness of the aryl
groups. The alkynylborates 1o and 1p prepared from tris(2,6-
dimethoxyphenyl)borane were considerably more reactive than
triphenyl(phenylethynyl)borate (1f), so that the palladium-
catalyzed reaction with allyl bromide proceeded even at
room temperature. The phenylethynylborate 1o gave isolable
alkenylborane 4o in 90% yield in a stereoselective manner
(E/Z = 95/5, eq 9). The stereochemistry of the major isomer
was determined as E by NOE analysis. The (cyclohexenyl-
ethynyl)borate 1p also provided the corresponding alkenylbor-
ane 4p in 93% yield (eq 10). The higher reactivity could be
attributed to the electron-rich nature of the 2,6-dimethoxy-
phenyl group. This accelerating electronic effect is in line with
the slower reaction rate observed with tris(4-fluorophenyl)-
borate 1i (Table 3, Entry 7). The high stereoselectivity might
be due to the sterics of the methoxy groups on ortho-positions
because the methoxy group on the para-position did not affect
the stereoselectivity (Scheme 2). Concerning the stability of the
produced alkenylboranes 4o and 4p, no decomposition was
observed during isolation by column chromatography on silica
gel. The stability is to be ascribed to steric hindrance of the 2,6-
dimethoxyphenyl groups rather than to intramolecular coordi-
93%
E/
Z
= 42/58
2.5 mol% [Pd2dba3]·CHCl3
6 mol% XANTPHOS
H
AcOH
Br
1c
+
ð6Þ
nC5H11 Ph
toluene, 70 °C
9
71%
E/Z = 53/47
We then examined the use of dialkyl(alkynyl)(aryl)borates in
the Pd/XANTPHOS-catalyzed reaction with allyl bromide.
The 9-BBN derivative 1m was reactive enough at room
temperature to provide trisubstituted alkene 5a in 30% yield
after hydrolysis (eq 7).22 The low yield is ascribed to the
formation of many other unidentified products. Better stereo-
selectivity was observed with 5a (E/Z = 10/90) than that of
the reaction of the corresponding alkynyltriphenylborate 1a.
An attempt to isolate the alkenyl-9-BBN 4m failed due to
instability toward air.
5 mol%
Ph
[Pd(π-allyl)Cl(xantphos)]
Ph(CH2)2
B
Br
[Me4N]
+
toluene, rt
1m
1
Ph
B
nation of the methoxy group to boron. In the H NMR spectra
Ph
AcOH
ð7Þ
of 4o and 4p, the two methoxy signals on each aryl group were
observed as equivalent. In the 11B NMR spectra, no up-field
shift was observed (¤ 68.6 for 4o, ¤ 67.1 for 4p). Thus,
intramolecular coordination is unlikely.
H
Ph
Ph
5a
30%
4m
E/Z = 10/90
Next, alkynylarylborate 1n having a 9-borabicyclo[3.3.2]-
decane (9-BBD) framework23,24 was tested (eq 8). The borate
1n was treated with allyl bromide in the presence of [Pd(³-
allyl)Cl(xantphos)], and the reaction mixture was directly
subjected to column chromatography on silica gel to afford a
mixture of alkenylboranes 4n (38% yield) and 10 (28% yield).
Thus, the produced alkenylboranes 4n and 10 were stable
enough to be isolated by column chromatography. The
structures of 4n and 10 were determined by NMR analyses
(COSY, NOESY, HSQC, and HMBC).25 The better stability of
4n and 10 than 4m is probably due to the steric hindrance
around the boron center caused by the bulky trimethylsilyl
group. Alkenyl-9-BBD 4n was formed through allylation at
the ¢-alkynyl carbon and 1,2-phenyl migration from boron to
the ¡-carbon as described above. Not only the phenyl group
but also the bridgehead sp3 carbon of the rigid 9-BBD
framework migrated, resulting in the formation of 10 with the
enlarged bicyclic skeleton appended by an exo-alkylidene
moiety. Thus, comparable migrating abilities of the aryl group
and the alkyl group of 1n under the reaction conditions were
demonstrated.
5 mol%
Ar
[Pd(π-allyl)Cl(xantphos)]
Br
[Me4N][Ph
BAr3]
+
ð9Þ
Ph
BAr2
toluene, rt
1o
4o
90%
MeO
E/Z = 95/5
Ar =
MeO
5 mol%
Ar
[Pd(π-allyl)Cl(xantphos)]
Br
[Me4N][
BAr ]
+
ð10Þ
3
toluene, rt
BAr2
1p
4p
93%
E/Z = 95/5
Finally, we examined the reactivity of alkenylborane 4o.
Treatment of 1,4-dienylborane 4o with DBU (20 mol %) caused
a shift of the carbon-carbon double bond to afford 1,3-
dienylborane 11 as a single stereoisomer in 81% yield (eq 11).
The steric hindrance around the boron atom would suppress the
complexation with DBU and the ³-accepting ability of the
vacant p-orbital of boron facilitates deprotonation, invoking
isomerization to the conjugate system with control of stereo-

1384 Bull. Chem. Soc. Jpn. Vol. 83, No. 11 (2010)
Pd-Catalyzed Allylation of Alkynylborates
chemistry.26 Treatment of 4o with 1.0 M HCl in methanol
caused site-selective protonolysis of the 2,6-dimethoxyphenyl-
boron linkages without cleavage of the alkenyl-boron linkage,
giving alkenylboronic acid 12 together with the corresponding
boroxin.27 After esterification with pinacol, boronic ester 13
was obtained in 90% yield with retention of the stereo-
chemistry (E/Z = >95/5, eq 12).
material is available free of charge on the web at: http://
www.csj.jp/journals/bcsj/.
References
1
Reviews: a) C. D. Entwistle, T. B. Marder, Chem. Mater.
2004, 16, 4574. b) S. Yamaguchi, A. Wakamiya, Pure Appl. Chem.
2006, 78, 1413. c) F. Jäkle, Coord. Chem. Rev. 2006, 250, 1107.
MeO
2
a) G. Zweifel, G. M. Clark, T. Leung, C. C. Whitney,
20 mol% DBU
toluene, reflux
Ar
Ar
ð11Þ
J. Organomet. Chem. 1976, 117, 303. b) J. J. Eisch, J. E. Galle, S.
Kozima, J. Am. Chem. Soc. 1986, 108, 379. c) P. H. M. Budzelaar,
S. M. Van der Kerk, K. Krogh-Jespersen, P. v. R. Schleyer, J. Am.
Chem. Soc. 1986, 108, 3960. d) J. J. Eisch, B. Shafii, J. D. Odom,
A. L. Rheingold, J. Am. Chem. Soc. 1990, 112, 1847. e) Y.-G.
Byun, S. Saebo, C. U. Pittman, Jr., J. Am. Chem. Soc. 1991, 113,
3689. f) Y. Sugihara, T. Yagi, I. Murata, A. Imamura, J. Am. Chem.
Soc. 1992, 114, 1479. g) U. Salzner, J. B. Lagowski, P. G. Pickup,
R. A. Poirier, Synth. Met. 1998, 96, 177.
Ar =
Ph
BAr2
Ph
BAr2
MeO
4o
E/Z = 95/5
11
81%
E
/Z
= >95/5
HCl
MeOH, rt
Ar
4o
E/Z = 95/5
+
boroxin
Ph
B(OH)2
12
Ar
B
3
a) H. Doi, M. Kinoshita, K. Okumoto, Y. Shirota, Chem.
pinacol, pTSA
ð12Þ
Mater. 2003, 15, 1080. b) W. L. Jia, X. D. Feng, D. R. Bai, Z. H.
Lu, S. Wang, G. Vamvounis, Chem. Mater. 2005, 17, 164.
THF, rt
Ph
O
O
4
a) S. Yamaguchi, T. Shirasaka, S. Akiyama, K. Tamao,
J. Am. Chem. Soc. 2002, 124, 8816. b) A. Sundararaman, M.
Victor, R. Varughese, F. Jäkle, J. Am. Chem. Soc. 2005, 127,
13748.
13
90%
E/Z = >95/5
Conclusion
5
Z. Yuan, C. D. Entwistle, J. C. Collings, D. Albesa-Jové,
A. S. Batsanov, J. A. K. Howard, N. J. Taylor, H. M. Kaiser, D. E.
Kaufmann, S.-Y. Poon, W.-Y. Wong, C. Jardin, S. Fathallah, A.
Boucekkine, J.-F. Halet, T. B. Marder, Chem.®Eur. J. 2006, 12,
2758.
In this paper, we described the palladium-catalyzed allylation
reaction of alkynyl(aryl)(diorganyl)borates. A palladium(0)
complex ligated by XANTPHOS was an active catalyst for
the allylation reaction to give alkenylboranes as a mixture of
stereoisomers. When a bulky 2,6-dimethoxyphenyl group was
employed as the substituent on boron, the palladium-catalyzed
allylation reaction proceeded stereoselectively to give air-stable
1,4-dienylboranes, which were selectively hydrolyzed by acid
to give the corresponding boronic acids.
6
Z.-Q. Liu, Q. Fang, D.-X. Cao, D. Wang, G.-B. Xu, Org.
Lett. 2004, 6, 2933.
7
A. Suzuki, H. C. Brown, Organic Synthesis via Boranes,
Aldrich, Milwaukee, WI, 2003.
8
9
Review: E. Negishi, J. Organomet. Chem. 1976, 108, 281.
a) P. Binger, R. Köster, Tetrahedron Lett. 1965, 6, 1901.
b) N. Miyaura, T. Yoshinari, M. Itoh, A. Suzuki, Tetrahedron Lett.
1974, 15, 2961. c) H. C. Brown, A. B. Levy, M. M. Midland,
J. Am. Chem. Soc. 1975, 97, 5017. d) A. Pelter, C. R. Harrison,
C. Subrahmanyam, D. Kirkpatrick, J. Chem. Soc., Perkin Trans. 1
1976, 2435.
10 a) P. Binger, Angew. Chem., Int. Ed. Engl. 1967, 6, 84. b) A.
Pelter, T. W. Bentley, C. R. Harrison, C. Subrahmanyam, R. J.
Laub, J. Chem. Soc., Perkin Trans. 1 1976, 2419. c) A. Pelter, K. J.
Gould, C. R. Harrison, J. Chem. Soc., Perkin Trans. 1 1976, 2428.
11 M. Deng, Y. Tang, W. Xu, Tetrahedron Lett. 1984, 25,
1797.
12 M. Naruse, K. Utimoto, H. Nozaki, Tetrahedron 1974, 30,
3037.
13 P. Binger, R. Köster, J. Organomet. Chem. 1974, 73, 205.
14 J. Gerard, L. Hevesi, Tetrahedron 2001, 57, 9109.
15 a) P. Binger, R. Köster, Synthesis 1973, 309. b) J. Hooz, R.
Mortimer, Tetrahedron Lett. 1976, 17, 805.
Experimental
Palladium-Catalyzed Allylation of Alkynyltriarylborate
1a. A Typical Procedure. Under an argon atmosphere, a
toluene solution (0.5 mL) of tetramethylammonium alkynyl-
triarylborate 1a (89.0 mg, 0.20 mmol), [Pd2dba3]¢CHCl3
(5.2 mg, 5 ¯mol), and XANTPHOS (6.9 mg, 12 ¯mol) was
stirred for 30 min at room temperature. To the solution was
added allyl bromide (28.8 mg, 0.24 mmol) in toluene (0.5 mL).
After being stirred at 70 °C for 15 min, AcOH (1 mL) was
added at room temperature. After 3 h, the reaction mixture was
neutralized with Na2CO3 solution. The aqueous layer was
extracted with AcOEt (3 times), washed with water (once),
brine (once), dried over MgSO4 and concentrated. The residue
was purified by preparative thin-layer chromatography on silica
gel (hexane) to afford the trisubstituted alkene 5a (44.5 mg,
0.18 mmol, 91% yield, E/Z = 54/46).
16 a) Y. Chen, N. Li, M. Deng, Tetrahedron Lett. 1990, 31,
2405. b) Y. Chen, M. Deng, N. Shi, Chin. Sci. Bull. 1991, 36, 570.
17 a) N. Ishida, T. Miura, M. Murakami, Chem. Commun.
2007, 4381. b) N. Ishida, Y. Shimamoto, M. Murakami, Org. Lett.
2009, 11, 5434.
This work was supported by Grant-in-Aid for Science
Research on Priority Areas (No. 19027032, Synergy of
Elements) from MEXT, Japan.
18 N. Ishida, M. Narumi, M. Murakami, Org. Lett. 2008, 10,
1279.
Supporting Information
Other experimental procedures and spectral data of new
compounds are described in the Supporting Information. This
19 A. M. Johns, M. Utsunomiya, C. D. Incarvito, J. F. Hartwig,
J. Am. Chem. Soc. 2006, 128, 1828.

N. Ishida et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 11 (2010) 1385
J. Am. Chem. Soc. 2005, 127, 8044.
24 The borate 1o was diastereoselectively synthesized from
commercially available B-MeO-10-TMS-9-BBD by a substitution
reaction with phenylmagnesium bromide followed by addition
of alkynyllithium. The sterically less demanding alkynyl group
located syn to bulky trimethylsilyl group.
25 See experimental section in detail.
26 A. Pelter, B. Singaram, L. Williams, J. W. Wilson,
Tetrahedron Lett. 1983, 24, 623.
27 For precedence in which electron-rich aromatic groups on
boron were selectively hydrolyzed by acids, see: A. Pelter, R.
Drake, Tetrahedron 1994, 50, 13801.
20 An indolyltriethylborate directly attacked a ³-allyl ligand
from the opposite side of palladium: M. Ishikura, H. Kato,
Tetrahedron 2002, 58, 9827.
21 [(o-tol)3PPd(aryl)Br]2 was reacted with amine HNR2 to
form a tetracoordinated (o-tol)3P(HNR2)Pd(aryl)Br. a) F. Paul, J.
Patt, J. F. Hartwig, J. Am. Chem. Soc. 1994, 116, 5969. b) R. A.
Widenhoefer, H. A. Zhong, S. L. Buchwald, Organometallics
1996, 15, 2745.
22 Isolated complex [Pd(³-allyl)Cl(xantphos)] was employed
in place of [Pd2dba3]¢CHCl3 and XANTPHOS because of the ease
of product isolation, although the [Pd2dba3]¢CHCl3/XANTPHOS
system gave similar results.
23 C. H. Burgos, E. Canales, K. Matos, J. A. Soderquist,