Stereoselective 1,4-silaboration of 1,3-dienes catalyzed by nickel complexes

Article abstract of DOI:10.1021/ol990908y

(matrix presented). The silicon-boron bond of (dimethylphenylsilyl)pinacolborane was stereoselectively added to acyclic 1,3-dienes in a 1,4-fashion to give (Z)-4-boryl-1-silyl-2-alkene derivatives in the presence of a Ni(0) catalyst generated from Ni(acac

Full text of DOI:10.1021/ol990908y

ORGANIC
LETTERS
1999
Vol. 1, No. 10
1567-1569
Stereoselective 1,4-Silaboration of
1,3-Dienes Catalyzed by Nickel
Complexes
Michinori Suginome, Takanori Matsuda, Takayo Yoshimoto, and Yoshihiko Ito*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of
Engineering, Kyoto UniVersity, Kyoto 606-8501, Japan
yoshi@sbchem.kyoto-u.ac.jp
Received August 4, 1999
ABSTRACT
The silicon−boron bond of (dimethylphenylsilyl)pinacolborane was stereoselectively added to acyclic 1,3-dienes in a 1,4-fashion to give (Z)-
4-boryl-1-silyl-2-alkene derivatives in the presence of a Ni(0) catalyst generated from Ni(acac)2 and diisobutylaluminum hydride. 1,4-Silaboration
of cyclic 1,3-dienes required the use of cyclohexyldiphenylphosphine with the Ni(0) catalyst to afford cis-4-boryl-1-silyl-2-cycloalkene derivatives
in high yields with high stereoselectivities.
Transition-metal catalyzed insertion reactions of carbon-
carbon multiple bonds to inter-element σ-bonds such as Si-
Si,1 Si-Sn,2 and B-B3 have provided powerful methods for
the preparation of organometallic compounds containing
multiple metallic elements in regio- and stereodefined
fashions. The synthetic applications of these organometallic
compounds have been extensively explored.4,5
We have reported regioselective additions of the silicon-
boron bond of silylboranes to alkynes6 and alkenes,7 which
are catalyzed by palladium and platinum complexes. More-
over, silaboration of 1,3-dienes was found to be catalyzed
by a platinum complex, giving 1,4-conjugate adducts as a
1:1 mixture of the corresponding Z- and E-isomers.8 Re-
(4) For recent reviews on the synthetic utilization of organosilicon
compounds, see: (a) Langkopf, E.; Schinzer, D. Chem. ReV. 1995, 95, 1375.
(b) Fleming, I.; Barbero, A.; Walter, D. Chem. ReV. 1997, 97, 2063. For
organotin compounds, see: (c) Mitchell, T. N. Synthesis 1992, 803. (d)
Marshall, J. A. Chem. ReV. 1996, 96, 31. For organoboron compounds,
see: (e) Brown, H. C.; Ramachandran, P. V. Pure Appl. Chem. 1991, 63,
307. (f) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.
(5) For examples of the use of bis-silylation for stereoselective organic
synthesis, see: (a) Murakami, M.; Suginome, M.; Fujimoto, K.; Nakamura,
H.; Andersson, P. G.; Ito, Y. J. Am. Chem. Soc. 1993, 115, 6487. (b)
Suginome, M.; Yamamoto, Y.; Fujii, K.; Ito, Y. J. Am. Chem. Soc. 1995,
117, 9608. (c) Suginome, M.; Iwanami, T.; Ito, Y. J. Org. Chem. 1998, 63,
6096.
(6) (a) Suginome, M.; Nakamura, H.; Ito, Y. Chem. Commun. 1996, 2777.
(b) Suginome, M.; Matsuda, T.; Nakamura, H.; Ito, Y. Tetrahedron 1999,
55, 8787. See also: Onozawa, S.-y.; Hatanaka, Y.; Tanaka, M. Chem.
Commun. 1997, 1229.
(7) Suginome, M.; Nakamura, H.; Ito, Y. Angew. Chem., Int. Ed. Engl.
1997, 36, 2516.
(1) (a) Horn, K. A. Chem. ReV. 1995, 95, 1317. (b) Sharma, H. K.;
Pannell, K. H. Chem. ReV. 1995, 95, 1351. (c) Suginome, M.; Ito, Y. J.
Chem. Soc., Dalton Trans. 1998, 1925.
(2) (a) Mitchell, T. N.; Killing, H.; Dicke, R.; Wickenkamp, R. J. Chem.
Soc., Chem. Commun. 1985, 354. (b) Chenard, B. L.; Laganis, E. D.;
Davidson, F.; RajanBabu, T. V. J. Org. Chem. 1985, 50, 3666. (c) Tsuji,
Y.; Obora, Y. J. Am. Chem. Soc. 1991, 113, 9368. (d) Murakami, M.;
Yoshida, T.; Kawanami, S.; Ito, Y. J. Am. Chem. Soc. 1995, 117, 6408 and
references therein.
(3) (a) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J. Am. Chem.
Soc. 1993, 115, 11018. (b) Baker, R. T.; Nguyen, P.; Marder, T. B.;
Westcott, S. A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1336. (c) Ishiyama,
T.; Yamamoto, M.; Miyaura, N. Chem. Commun. 1996, 2073. (d) Ishiyama,
T.; Yamamoto, M.; Miyaura, N. Chem. Commun. 1997, 689. (e) Clegg,
W.; Johann, T. R. F.; Marder, T. B.; Norman, N. C.; Orpen, A. G.; Peakman,
T. M.; Quayle, M. J.; Rice, C. R.; Scott, A. J. J. Chem. Soc., Dalton Trans.
1998, 1431 and references therein.
10.1021/ol990908y CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/19/1999

cently, we found that nickel complexes were also able to
activate the silicon-boron bond, promoting a silaborative
dimerization of alkynes.9 This finding opened up new
possibilities in bismetalation chemistry, since nickel catalysts
have scarcely been employed for activation of inter-element
σ-bonds.10 Herein, we wish to report that nickel complexes
catalyzed the stereoselective 1,4-addition of the silicon-
boron bond of silylborane to acyclic as well as cyclic 1,3-
dienes effectively. The 1,4-silaboration produced stereo-
defined 4-boryl-1-silyl-2-alkene derivatives having both
allylsilane and allylborane moieties, which were utilized in
selective allylation of aldehydes and ketones.
the platinum-phosphine complex also promoted the 1,4-
conjugate addition with low stereoselectivity (entry 3). The
palladium-1,1,3,3-tetramethylbutyl isocyanide (t-OcNC)
complex, which was most effective for the silaboration of
alkynes, did not give any adducts (entry 2).13 The yield for
the 1,4-silaboration adducts depended markedly upon the
substituents on the boron atom of the silylborane. For
example, the reaction of bis(diethylamino)(dimethylphenyl-
silyl)borane with 2a was sluggish in the presence of either
the nickel or platinum catalyst.14
The nickel-catalyzed 1,4-silaborations of some 1,3-dienes
2b-d are summarized in Table 2.15 Isoprene (2b) reacted
Reactions of 2,3-dimethyl-1,3-butadiene (2a) with (di-
methylphenylsilyl)pinacolborane (1) were carried out in the
presence of a catalytic amount of group 10 metal (Ni, Pd,
and Pt) complexes (Table 1).
Table 2. Nickel-Catalyzed 1,4-Silaboration of 1,3-Dienes
2b-da
Table 1. Reaction of Silylborane 1 with
2,3-Dimethyl-1,3-butadiene (2a) in the Presence of Nickel,
Palladium, and Platinum Complexesa
a
Silylborane 1 (1 equiv) and 2b-d (2 equiv) were reacted in the
entry
catalystb
temp/°C
yield/%c
Z/Ed
presence of Ni(acac)2 (0.05 equiv) and DIBAH (0.10 equiv) in toluene at
b
80 °C for 24 h unless otherwise noted. Ratios of 3 and 4 were determined
by 1H NMR. The reaction was carried out under 1 atm of 1,3-butadiene.
c
1
2
3
Ni(acac)2-DIBAH
Pd(OAc)2-t-OcNC
Pt(CH2dCH2)(PPh3)2
80
110
110
90
0
95
>99/1
48/52
with 1 to give 3b and 4b in 92% combined yield with high
stereoselectivity but only moderate regioselectivity (3b/4b
) 72/28). 2-Methyl-1,3-pentadiene (2c) afforded 3c (56%)
and 4c (28%) with slightly lower regioselectivity than that
of 2b. Silaboration of gaseous 1,3-butadiene (2d) also
proceeded under atmospheric pressure to give 3d in high
yield. Almost no reactions were detected with 1,1- and 1,4-
disubstituted 1,3-dienes such as 4-methyl-1,3-pentadiene and
2,4-hexadiene, respectively, under the same reaction condi-
tions.
a
Silylborane 1 (1 equiv) and 2a (2 equiv) were heated in the presence
of Ni (0.05 equiv), Pd (0.02 equiv), or Pt (0.02 equiv) catalyst in toluene
for 24 h. Ni/DIBAH ) 1/2; Pd/isocyanide ) 1/15. Isolated yield by
bulb-to-bulb distillation. Determined by H NMR.
b
c
d
1
The nickel catalyst, generated in situ by mixing Ni(acac)2
with diisobutylaluminum hydride (DIBAH), was most ef-
fective for the stereoselective silaboration of 2a, affording
1,4-silaboration product 3a with Z-stereochemistry as the sole
product in 90% yield (entry 1).11 Neither the 1,2-addition
product3d nor the silaborative dimerization product12 was
detected in the reaction mixture. As previously reported,8
Compounds 3a and 3d thus obtained were reacted with
benzaldehyde to give 5a and 5d stereoselectively (Scheme
(12) For transition-metal catalyzed bismetalative dimerization of 1,3-
dienes, see: (a) Sakurai, H.; Kamiyama, Y.; Nakadaira, Y. Chem. Lett.
1975, 887. (b) Obora, Y.; Tsuji, Y.; Kawamura, T. Organometallics 1993,
12, 2853. (c) Obora, Y.; Tsuji, Y.; Kakehi, T.; Kobayashi, M.; Shinkai, Y.;
Ebihara, M.; Kawamura, T. J. Chem. Soc., Perkin Trans. 1 1995, 599 and
references therein. See also ref 3c.
(8) Suginome, M.; Nakamura, H.; Matsuda, T.; Ito, Y. J. Am. Chem.
Soc. 1998, 120, 4248.
(9) Suginome, M.; Matsuda, T.; Ito, Y. Organometallics 1998, 17, 5233.
(10) (a) Okinoshima, H.; Yamamoto, K.; Kumada, M. J. Am. Chem. Soc.
1972, 94, 9263. (b) Jzang, T. T.; Liu, C.-S. Main Group Met. Chem. 1987,
10, 373. (c) Ishikawa, M.; Nishihara, Y.; Sakamoto, H.; Ono, T.; Oshita, J.
Organometallics 1992, 11, 483.
(13) Palladium-phosphine and palladium-phosphite complexes were
also ineffective for the reaction.
(11) Typical Procedure for the Nickel-Catalyzed 1,4-Silaboration of
1,3-Dienes. To a mixture of Ni(acac)2 (25.7 mg, 0.10 mmol) and 1,3-diene
(2 equiv based on 1) in a Schlenk tube was added DIBAH (0.2 M solution
in toluene, 1.0 mL) at 0 °C. The mixture was stirred for 30 min at 0 °C. To
the mixture was added 1 (521 mg, 2.0 mmol); the mixture was heated at
80 °C for 24 h. Evaporation of volatile materials followed by bulb-to-bulb
distillation afforded the products.
(14) The reaction of 1,3-dienes with a stannylborane having nitrogen
groups on the boron atom is effectively catalyzed by a palladium-phosphite
complex. See: Onozawa, S.-y.; Hatanaka, Y.; Tanaka, M. Tetrahedron Lett.
1998, 39, 9043.
(15) The regio- and stereochemical assignments were made by NOE
experiments of the silaboration products or by transformation to homoallylic
alcohols through reactions with benzaldehyde.
1568
Org. Lett., Vol. 1, No. 10, 1999

isomer 7a′ as the minor product. Although dimethylphenyl-
phosphine also worked as a ligand to give the products in
high yield, the stereoselectivity was exceptionally low (entry
3). The use of methyldiphenylphosphine gave the silaboration
products in high yield with stereoselectivity similar to that
with P(n-Bu)3 (entry 4). Almost complete stereoselectivity
with a quantitative yield was attained by using the more
sterically congested cyclohexyldiphenylphosphine ligand
(entry 5).17 No reaction occurred when triphenylphosphine
was used as the ligand (entry 6). It may be noted that a
platinum-triphenylphosphine complex also catalyzed the
reaction, affording 7a stereoselectively in low yield (entry
7).
Scheme 1
1). On the basis of the stereochemistry of 5, the Z geometry
of 3 was confirmed unambiguously.16
Although various bismetalations of acyclic dienes have
been reported so far, only a few examples have been known
for cyclic dienes.3e,10b,c The nickel catalyst generated from
Ni(acac)2 and DIBAH did not promote the silaboration of
1,3-cyclohexadiene. However, it was found that the use of
the appropriate phosphine ligand on nickel remarkably
increased the catalytic activity as well as the stereoselectivity
of the silaboration (Table 3).
The reaction conditions were applicable to 1,3-cyclohepta-
diene (6b), providing 7b in 93% yield with complete stereo-
selectivity (Scheme 2). However, cyclopentadiene and 1,3-
Scheme 2
Table 3. 1,4-Silaboration of 1,3-Cyclohexadiene (6a) with 1a
cyclooctadiene were inert toward the reaction under identical
reaction conditions.
Although the mechanism for formation of the trans-isomer
in the silaboration of cyclic 1,3-dienes is not clear at this
moment, acceleration of the reductive elimination step by
sterically bulky phosphine ligands such as P(c-Hex)Ph2 may
be the key for the observed high stereoselectivity.
In summary, the stereoselective addition of the silicon-
boron bond of silylborane to 1,3-dienes was successfully
catalyzed by nickel(0) catalysts. The silaboration of cyclic
1,3-dienes proceeded with perfect stereoselectivity with the
appropriate choice of the phosphine ligand.
entry
phosphine
yield/%b
cis/transc
1
2
3
4
5
6
7
none
0
39
92d
97
99
0
P(n-Bu)3
PMe2Ph
PMePh2
P(c-Hex)Ph2
PPh3
94/6
60/40
93/7
>99/1
e
21
>99/1
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Areas (The
Chemistry of Inter-Element Linkage) from the Ministry of
Education, Science, Sports, and Culture, Japan. T.M. thanks
fellowship support from the Japan Society for the Promotion
of Science for Young Scientists.
a
A mixture of 1 (1 equiv), 6a (2 equiv), Ni(acac)2 (0.05 equiv), DIBAH
(0.10 equiv), and phosphine (0.10 equiv) was heated in toluene at 80 °C
b
c
for 24 h unless otherwise noted. Isolated yield. Ratios of cis- and trans-
isomers were determined by HPLC. Contaminated with a small amount
of byproducts. Use of Pt(CH2dCH2)(PPh3)2 (0.02 equiv) instead of Ni
catalysts.
d
e
Supporting Information Available: Experimental pro-
cedures and characterization data for the new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
The nickel catalyst bearing tributylphosphine induced the
silaboration of 1,3-cyclohexadiene, but only in 39% yield
(entry 2). cis-4-Boryl-1-silyl-2-cyclohexene 7a was formed
as the major product together with the corresponding trans-
OL990908Y
(16) (a) Hoffmann, R. W.; Zeiss, H.-J. Angew. Chem., Int. Ed. Engl.
1979, 18, 306. (b) Hoffmann, R. W.; Zeiss, H.-J. J. Org. Chem. 1981, 46,
1309.
(17) The reaction afforded 7a in 80% yield in the presence of 2 mol %
of the Ni catalyst.
Org. Lett., Vol. 1, No. 10, 1999
1569