Transformation of aldehydes into (E)-1-alkenylsilanes and (E)-1-alkenylboronic esters with a catalytic amount of a chromium salt

Article abstract of DOI:10.1246/bcsj.77.1581

(Diiodomethyl)trimethylsilane (Me₃SiCHI₂, 1) is produced by treatment of iodoform with manganese in the presence of Me ₃SiCl. Aldehydes are converted to (E)-1-trimethylsilyl-1-alkenes in a stereoselective manner with a geminal dichromium reagent generated from 1, manganese, Me₃SiCl, and a catalytic amount of CrCl ₃[thf]₃ in THF. Similarly, (E)-1-alkenylboronic esters are prepared stereoselectively in good to excellent yields by treatment of aldehydes with a geminal dichromium reagent derived from Cl₂CHB(OR) ₂ [(OR)₂ = OCMe₂CMe₂O] and LiI instead of 1.

Full text of DOI:10.1246/bcsj.77.1581

Ó 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 1581–1586 (2004) 1581
Transformation of Aldehydes into (E)-1-Alkenylsilanes and (E)-1-
Alkenylboronic Esters with a Catalytic Amount of a Chromium Salt
ꢀ
Kazuhiko Takai, Yuji Kunisada, Yukiko Tachibana, Nana Yamaji, and Emi Nakatani
Department of Applied Chemistry, Faculty of Engineering, Okayama University, Tsushima, Okayama 700-8530
Received March 5, 2004; E-mail: ktakai@cc.okayama-u.ac.jp
(Diiodomethyl)trimethylsilane (Me3SiCHI2, 1) is produced by treatment of iodoform with manganese in the pres-
ence of Me3SiCl. Aldehydes are converted to (E)-1-trimethylsilyl-1-alkenes in a stereoselective manner with a geminal
dichromium reagent generated from 1, manganese, Me3SiCl, and a catalytic amount of CrCl3[thf]3 in THF. Similarly, (E)-
1-alkenylboronic esters are prepared stereoselectively in good to excellent yields by treatment of aldehydes with a gemi-
nal dichromium reagent derived from Cl2CHB(OR)2 [(OR)2 = OCMe2CMe2O] and LiI instead of 1.
Alkenylsilanes and -boronic esters are important synthetic
intermediates for stereoselective carbon–carbon bond forma-
tion. The silanes and boronic esters having E-configuration
are usually prepared by hydrosilylation and -boration of termi-
nal alkynes, respectively.1,2 We reported a preparative method
for (E)-alkenylsilanes from aldehydes with a geminal dichro-
mium reagent derived from Me3SiCHBr2 and CrCl2 in 1987,3
and a method for (E)-alkenylboronic esters with a reagent de-
rived from a (dichloromethyl)boronic ester, CrCl2, and LiI in
1995.4 Although these methods provide functionalized olefins
of E-configuration almost exclusively with one-carbon exten-
sion under mild conditions, the transformations use stoichio-
metric amounts of the one-electron reductant, CrCl2. Following
the report of the catalytic cycle of chromium(II) assembled by
Me3SiCHBr2 should be prepared in advance by deprotonation
and silylation from dibromomethane, which requires using a
strong base at a carefully controlled low temperature.9
At first, we examined a chromium-catalyzed reaction using
manganese for reduction of chromium(III) and Me3SiCl for re-
generation of chromium(II).5 In contrast to the stoichiometric
reaction (Table 1, entry 1), the yield of 2 decreased to 42%,
and 3-phenylpropanal was recovered in only 19% yield (entry
3). Addition of LiI to the reaction mixture accelerated the trans-
formation, and the reaction completed in 6 h to give 2 in 60%
yield (entry 4). The result suggests that Me3SiCHI2 (1), which
could be produced in the mixture, is better suited for the cata-
lytic reaction than Me3SiCHBr2. Therefore, we examined a
preparative method with 1. Treatment of 3-phenylpropanal
with 1 (2 equiv.), manganese (6 equiv.), Me3SiCl (6 equiv.),
and chromium(II) chloride (0.16 equiv.) at 25 ꢁC for 20 h
afforded 2 in 87% yield (entry 5). Zinc also reduces chro-
mium(III) to chromium(II) and can be used for a catalytic ver-
sion of (E)-iodoalkene formation from aldehydes.6 However,
when zinc was used for the synthesis of 2, the yield was some-
what lower than that obtained with manganese (entry 6). Be-
cause chromium(III) is reduced with manganese to give chro-
mium(II), readily available chromium(III) chloride could be
used for the reaction (entry 7). Handling a THF complex of
chromium(III), CrCl3[thf]3, is easier than handling anhydrous
chromium(III) chloride, especially in small-scale experiments,
due to lower hygroscopicity (entry 8). In addition, slow addi-
tion of both the aldehyde and Me3SiCHI2 to the mixture of
manganese, Me3SiCl, and a catalytic amount of CrCl3[thf]3
in THF over 4 h improved the yield from 75% to 86% (entry
9). In contrast to the stoichiometric reactions (entries 1 and
2), the formation of a small amount of (Z)-alkenylsilane was
observed in the catalytic reactions (entries 3–10).
Furstner,5 we could reduce the amount of the chromium salt in
¨
the transformation of aldehydes to (E)-iodoalkenes using zinc
as a reductant.6 We disclose herein a procedure for the stereo-
selective preparation of (E)-alkenylsilanes and -boronic esters
from aldehydes with geminal dichromium reagents7 using a
catalytic amount of the chromium salts.
Results and Discussion
Preparation of (E)-Alkenylsilanes.
Treatment of
Me3SiCHBr2 with chromium(II) chloride in THF generates a
geminal dichromium reagent [Me3SiCH(CrX2)2, X = Cl or
Br], which reacts with aldehydes to give (E)-alkenylsilanes un-
der high stereocontrol (Scheme 1).3 A typical feature of the
transformation is that it can be performed under mild condi-
tions, leaving the coexisting ketone, ester, and silyl ether
groups unchanged. Thus, the method has been employed in sev-
eral natural product syntheses.8 However, the method still has
two disadvantages: First, 6–8 equiv. of chromium(II) chloride
are usually necessary to obtain reasonable yields. Second,
The results with Me3SiCHI2 and a catalytic amount of the
chromium(III) salt are summarized in Table 2. E-Isomers were
obtained selectively in all cases, probably due to the steric
factor of the trimethylsilyl group. A ketone carbonyl remained
unchanged after the reaction (Table 2, entry 5).
Me3SiCHBr2, CrCl2
Ph
2 86% (E / Z = >99 / <1)
Ph
SiMe3
CHO
THF, 25 °C, 24 h
Scheme 1.
In 1970, Seyferth reported a procedure for Me3SiCHI2 (1)
Published on the web August 6, 2004; DOI 10.1246/bcsj.77.1581

1582 Bull. Chem. Soc. Jpn., 77, No. 8 (2004)
Preparation of Alkenylsilanes and -Boronates
Table 1. Preparation of Trimethyl(4-phenyl-1-butenyl)silanea)
Me3SiCHX2, Cr(II)
Ph
Ph
SiMe3
CHO
THF, 25 °C
2
Me3SiCHX2
X, equiv.
Cr salt
equiv.
Metal
equiv.
Me3SiCl
equiv.
LiI
Entry
Time/h
Yield/%
E=Z
equiv.
1
2
Br, 2.0
I, 2.0
CrCl2, 8.0
CrCl2, 8.0
24
4
86
90
>99/<1
>99/<1
3
4
5
6
7
8
9
Br, 2.0
Br, 2.0
I, 2.0
I, 2.0
I, 2.0
I, 2.0
I, 2.0
CrCl2, 0.2
CrCl2, 0.2
CrCl2, 0.2
CrCl2, 0.2
CrCl3, 0.2
Mn, 6.0
Mn, 6.0
Mn, 6.0
Zn, 6.0
Mn, 6.0
Mn, 6.0
Mn, 6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
24
6
20
20
20
20
42c)
60
87
59
72
75
86
95/5
97/3
95/5
95/5
93/7
94/6
94/6
4.0
CrCl3[thf]3, 0.2
CrCl3[thf]3, 0.2
6 (4)b)
a) Reactions were conducted on a 2.0 mmol scale. Isolated yields. b) Time for adding a solution of 3-phenylpropanal and
Me3SiCHI2 in THF is shown in parenthesis. c) 3-Phenylpropanal was recovered in 19% yield.
iodine atoms are reduced to give a geminal dichromium reagent
(ICH(CrX2)2, X = I or Cl).7b The yield of 1 improved to 47%
when DME was used as a solvent, and diiodomethane was ob-
tained in 7% yield (entry 2). Although the amount of 1 increas-
ed to 52% yield when a catalytic amount of sodium iodide was
added and DMF was used as a co-solvent (DME–DMF, 4:1),
further reduction of 1 and silylation occurred to give
(Me3Si)2CHI (4) in 6% yield (entry 4). Because it is difficult
to remove 4 from 1 by distillation, we choose to use the reaction
in only DME for large scale preparation. It is worth noting that
the manganese-mediated process (entry 2) is exothermic, and it
is important to keep the reaction mixture below 25 ꢁC by using
a water bath. The dimer 3 was produced as the main product
when the reaction temperature was allowed to increase to
50 ꢁC (entry 3).
Preparation of (E)-Alkenylboronic Esters. (E)-1-Alke-
nylboronic esters were prepared stereoselectively from alde-
hydes with one-carbon extension with a geminal dichromium
reagent derived from a (dichloromethyl)boronic ester 6,12
chromium(II) chloride, and LiI under mild conditions
(Scheme 2).4,13 Addition of LiI was indispensable to promote
the reaction; the aldehyde was recovered in 82% yield without
addition of LiI (Table 4, entries 1 and 2). Treatment of 6 with
LiI generated I2CHB(OCMe2)2 (8), which is easily reduced
with CrCl2 to give the corresponding geminal dichromium
reagent.
In order to generate chromium(II), we examined several met-
al reductants. Both zinc and manganese were found to be effec-
tive for assembling a catalytic cycle of the geminal dichromium
reagent. For example, treatment of 3-phenylpropanal with 6 (2
equiv.), LiI (4 equiv.), manganese (6 equiv.), Me3SiCl (6
equiv.), and chromium(II) chloride (0.2 equiv.) in THF at 25
ꢁC for 20 h gave the boronic ester 7 in 90% yield
(E=Z ¼ 95=5) (entry 3). The yield of 7 decreased to 71%
(E=Z ¼ 90=10) with zinc (6 equiv.) instead of manganese,
although the yield slightly increased to 80% (E=Z ¼ 89=11)
when the amount of chromium(II) chloride was increased to
0.3 equivalent (entry 4). The less-hygroscopic chromium(III)
salt CrCl3[thf]3 could also be employed for the alkenylboronic
Table 2. Transformation of Aldehydes into (E)-1-Alkenyl-
silanesa)
Me3SiCHI2, Mn
cat. CrCl3[thf]3, Me3SiCl
R
RCHO
SiMe3
THF, 25 °C, 6 h (slow addition, 4 h)
Entry
R
Yield/%b)
E=Z
1
2
3
4
5
Ph(CH2)2
86
94/6
95/5
94/6
91/9
95/5
87c)
77
c-C6H11
Ph
MeCO(CH2)8
88d)
82e)
a) Reactions were conducted on a 2.0 mmol scale. Me3SiCHI2
(3.0 mol), Mn (9.0 mol), Me3SiCl (9.0 mol), and CrCl3[thf]3
(0.20 mol) were used per mol of aldehyde. See the typical pro-
cedure in the experimental section. b) Isolated yields. (E)-Al-
kenylsilanes were produced exclusively. c) CrCl2 was used in-
stead of CrCl3[thf]3. A mixture of 3-phenylpropanal and iodo-
form in THF was added in one portion. d) GLPC yield. e)
Trimethyl[(E)-11-methyl-1,11-dodecadienyl]silane was pro-
duced in 14% yield.
using iodine–magnesium exchange of iodoform with isopropyl-
magnesium chloride followed by silylation.9a Another method
reported by Charreau in 1990 contained deprotonation of diio-
domethane with NaN(SiMe3)2.9b Both procedures require care-
fully controlled temperatures below ꢂ85 ꢁC to deal with the un-
stable carbenoid I2CHMtl (Mtl = MgX or Na); otherwise, 1,2-
bis(trimethylsilyl)ethene (3) is produced smoothly. We have re-
cently found a new preparative method for Me3SiCHI2 which is
conducted at ambient temperature.10
When iodoform was treated with manganese in THF in the
presence of an excess amount of Me3SiCl, the desired
Me3SiCHI2 was produced in 21% yield (Table 3, entry 1).
The formation of Me3SiCHI2 suggests that selective reduction
of one iodine atom of the iodoform and successive silylation
occur. Such selective reduction of iodoform leading to I2CHMtl
was also observed with SmI2;11 however, this reduction shows
a sharp contrast to the reduction with CrCl2 where two of the

K. Takai et al.
Bull. Chem. Soc. Jpn., 77, No. 8 (2004) 1583
Table 3. Preparation of (Diiodomethyl)trimethylsilanea)
Mn, Me3SiCl
+ (Me3Si)2CHI
+ CH2I2
Me3SiCHI2
CHI3
1 h
1
4
Me3Si
+ Me3SiCH2I +
SiMe3
5
3
Yield/%
Entry
Solvent
Temp/ꢁC
Recov.
CHI3
1
CH2I2
4
5
3
1
2
3
THF
DME
DME
25
25
21
47
0
3
7
0
0
0
0
0
0
0
3
0
34
0
3
0
25 to 50
(exothermic)
25
4
DME, DMFb)
(4:1)
52
0
6
3
0
0
a) Reactions were conducted on a 20 mmol scale. Mn (3.0 mol) and Me3SiCl (3.0 mol) were used per
mol of iodoform. b) NaI (0.3 mol) was added per mol of iodoform.
Table 4. Preparation of Pinacol 4-Phenyl-1-butenylboronatea)
O
Cl2CHB
O
, Cr(II)
O
O
Ph
Ph
B
CHO
THF, 25 °C
7
Cr salt
equiv.
Metal
equiv.
Me3SiCl
equiv.
LiI
Entry
Time/h
Yield/%
E=Z
equiv.
1
2
CrCl2, 8.0
CrCl2, 8.0
—
—
—
—
—
4.0
16
16
0b)
91
—
98/2
3
4
5
6
CrCl2, 0.20
CrCl2, 0.30
CrCl3[thf]3, 0.20
CrCl3[thf]3, 0.30
Mn, 6.0
Zn, 6.0
Mn, 6.0
Zn, 6.0
6.0
6.0
6.0
6.0
4.0
4.0
4.0
4.0
20
20
20
20
90
80
84
77
95/5
89/11
96/4
90/10
a) Reactions were conducted on a 1.0 mmol scale. Isolated yields. b) 3-Phenylpropanal was recovered in
82% yield.
of chromium(III) salt is shown in Scheme 3. The reduction of
O
O
RCHX2 with 4 equiv. of chromium(II) gives a geminal dichro-
mium reagent, which reacts with an aldehyde followed by elim-
ination of (X2Cr)2O to afford the functionalized alkene. The
produced (X2Cr)2O is converted to a chromium(III) halide with
an excess amount of Me3SiCl, and the chromium(III) is then
reduced with manganese to reproduce chromium(II).5 Two
equivalents of both manganese and Me3SiCl are necessary
for this transformation. A catalytic cycle is realized, because
the reduction rates of both 1 and 8 with manganese are consid-
erably slower than that with chromium(II).
High E-selectivity in the formation of alkenylsilanes and
-boronic esters with the gem-dichromium species is explained
by the mechanism depicted in Scheme 4. Addition of the
gem-dichromium species (RCH(CrLn)2) to an aldehyde
(R0CHO) proceeds via a six-membered pseudo-chair transition
state 10 containing two chromium ions bridged by a halogen.
Both substituents R and R0 possess stable equatorial positions
in the transition state. syn-Elimination of (LnCr)2O from the ad-
duct 11 takes place smoothly, before rotation at the formed sin-
gle bond, to give E-olefins. In the catalytic reactions, the coex-
Cl2CHB
CrCl2, LiI
O
O
6
Ph
Ph
B
CHO
THF, 25 °C
7
Scheme 2.
ester formation (entries 5 and 6).
Several examples of the transformation of aldehydes to the
corresponding 1-alkenylboronic esters are summarized in
Table 5. Reactions with manganese gave better yields and more
reproducible isomeric ratios than those with zinc. Aldehyde-
selective transformation of the keto aldehyde 9 was achieved
(Table 5, entry 5). Under the standard reaction conditions
(Table 5, entry 1, Mn), the following compounds were recov-
ered: 1-dodecene (94%); 1-dodecyne (93%); 1-chlorododecane
(95%); ethyl octanoate (95%); nonanenitrile (92%); nonanal
ethylene acetal (93%).
A plausible mechanism of the alkenylsilane and boronic es-
ter formation with manganese, Me3SiCl, and a catalytic amount

1584 Bull. Chem. Soc. Jpn., 77, No. 8 (2004)
Table 5. Transformation of Aldehydes to (E)-1-Alkenylboronic Estersa)
Preparation of Alkenylsilanes and -Boronates
O
Cl2CHB
, LiI, Mn (or Zn)
O
6
cat. CrCl3[thf]3, Me3SiCl
O
B
R
RCHO
O
THF, 25 °C, 20 h
Mnb)
Znc)
Entry
R
Yield/%d)
E=Ze)
Yield/%d)
E=Ze)
1
2
3
4
5
Ph(CH2)2
c-C6H11
t-Bu
84
92
93
88
80
96/4
97/3
96/4
96/4
97/3
77
90
88
67
52f)
90/10
94/6
98/2
92/8
87/13
Ph
MeCO(CH2)8 (9)
a) Reactions were conducted on a 1.0 mmol scale. b) Dichloromethylboronic ester (6, 2 mol), LiI (4
mol), manganese (6 mol), Me3SiCl (6 mol), and CrCl3[thf]3 (0.2 mol) were employed per mole of
an aldehyde. See the typical procedure in the experimental section. c) The ester 6 (2 mol), LiI (4
mol), zinc (6 mol), Me3SiCl (6 mol), and CrCl3[thf]3 (0.3 mol) were employed per mole of an aldehyde.
d) Isolated yields. e) The E=Z ratios of disubstituted olefins were determined by GLPC and/or 1H NMR
analysis. f) The keto aldehyde 9 was recovered in 13% yield.
R'CHO
H
CrX2
CrX2
R
H
L
CrX2
CrX2
R
H
H
Ln
Cr
C
RCHI2
C
X
L
CrLn
OCrLn
R
L
R = Me3Si (1)
Cr
Cr
R
R'
R'CHO
O
R'
or
X
2 CrX3
CrX2
L
O
B
O
H
L
L
+
R'
H
11
fast
4 CrX2
R
R = Me3Si (1)
L
2 CrX3
(8)
or
10
OCrX2
O
B
H
R'
2 MnX2
or 2 ZnX2
O
(X2Cr)2O
R
(8)
2 Mn
or 2 Zn
(Me3Si)2O
R'
H
R
2 Me3SiCl
Scheme 4.
Scheme 3.
and Fieser.15 Dry, oxygen-free tetrahydrofuran (THF) and dimeth-
oxyethane (DME) were purchased from Kanto Chemicals, Co.
Dry, oxygen-free N,N-dimethylformamide (DMF) was purchased
from Wako Pure Chemicals Co. Chlorotrimethylsilane was freshly
istent manganese (or zinc) ion generated in the reaction mixture
could partially replace the chromium ion in the transition state
10, which could cause the formation of a small amount of Z-
olefins.7a,14
ꢁ
distilled, bp 57–58 C. Distillations of small amounts of products
In conclusion, the amount of the chromium(II) salts needed
for the selective transformations of aldehydes to (E)-alkenyl-
silanes and -alkenylboronic esters can be reduced by using a
combination of manganese and Me3SiCl. Zinc can also be used
as a reductant in the formation of (E)-alkenylboronic esters
from aldehydes.
were performed with a Buchi Kugelrohr, and boiling points are in-
¨
dicated as an air bath temperature without correction. FT-IR spec-
´ ´
tra were obtained on a Bio-Rad FTS-7 or a Nicolet Protege 460
spectrometer. 1H and 13C NMR spectra were determined with a
Varian Gemini-200 or a JEOL JNM-LA400 instrument. Chemical
shifts are expressed in ppm downfield from internal tetramethyl-
silane using the ꢀ scale. Low and high resolution of EI mass spectra
were obtained with a capillary GC interfaced JEOL JMS-SX102A.
Column chromatography was performed on silica gel 60 (200–400
mesh) of Merck KGaA.
Experimental
General. Unless otherwise noted, materials were obtained
from commercial suppliers and were used without further purifica-
tion. Chromium(II) chloride (99.99% purity) was purchased from
Aldrich Chemical Co. The salt should be handled under an inert at-
mosphere. CrCl3[thf]3 (97% purity) was purchased from Aldrich
Chemical Co. and used without further purification. Lithium iodide
was dried at 120 ꢁC (2 Torr) for 1 day. Manganese powder was pur-
chased from either Rare Metallic Co. (99% purity, –80 mesh) or
Kojundo Chemical Laboratory (99.9% purity, –50 mesh) and
was used without further activation. Zinc dust (GR grade) was pur-
chased from E. Merck Co. (>95%), and was activated by washing
several times with 5% hydrochloric acid, washing in turn with wa-
ter, methanol, and ether, and drying in vacuo according to Fieser
Preparation of (Diiodomethyl)trimethylsilane in Large
Scale: A dry, 500-mL three-necked, round-bottomed flask was
equipped with a magnetic stirring bar, nitrogen inlet, rubber sep-
tum, and a 100-mL, graduated, pressure-equalizing addition funnel
that was sealed with a rubber septum. The flask was charged with
manganese powder (20 g, 0.36 mol) and dry DME (35 mL). Chlo-
rotrimethylsilane (46 mL, 0.36 mol) was added to the suspension
using a syringe at 25 ꢁC, and the mixture was stirred at 25 ꢁC
for 30 min. The addition funnel was charged with a solution of io-
doform (47 g, 0.12 mmol) in DME (120 mL), which was then add-
ed dropwise at 25 ꢁC (water bath) to the stirring solution over a pe-

K. Takai et al.
Bull. Chem. Soc. Jpn., 77, No. 8 (2004) 1585
tenylboronate (7)]:
riod of 2.5 h. The addition funnel was rinsed with dry DME (5 mL).
The resulting dark brown mixture was stirred at 25 ꢁC for an addi-
tional 30 min. The magnetic stirring bar was washed with hexane
(20 mL), and the whole mixture was poured into ice-cooled water
(100 mL). The quenching was a slightly exothermic process. The
whole mixture was passed through a short layer of CeliteÒ on a
200-mL suction filter, using hexane (100 mL) as an eluent. The
yellow organic layer that separated was washed with a sodium
thiosulfate (3 ꢃ 30 mL) and sodium chloride solution (3 ꢃ 30
mL), and then dried over anhydrous MgSO4. The solvent was re-
moved with a rotary evaporator. The crude product was distilled
to give 16.7–17.3 g (41–42%) of (diiodomethyl)trimethylsilane
(1), bp 63 ꢁC at 1.3 Torr reduced pressure. IR (neat): 2953,
Under an argon atmosphere, Me3SiCl
(0.76 mL, 6.0 mmol) was added at 25 ꢁC to a suspension of
CrCl3[thf]3 (75 mg, 0.20 mmol), manganese (0.33 g, 6.0 mmol),
and LiI (0.54 g, 4.0 mmol) in THF (7 mL). After the mixture
was stirred at 25 ꢁC for 30 min, a solution of 3-phenylpropanal
(0.13 g, 1.0 mmol) and (dichloromethyl)boronic ester 6 (0.42 g,
2.0 mmol) in THF (3 mL) was added at 25 ꢁC to the mixture over
a period of 4 h. The color of the mixture gradually turned from dark
green to dark brown during the addition. After being stirred for an
additional 2 h, the reaction mixture was filtered through a short pad
of CeliteÒ. The filtrate was poured into water (25 mL) and extract-
ed with ether (3 ꢃ 10 mL). The combined extracts were dried over
anhydrous Na2SO4 and concentrated. Purification by column chro-
matography on silica gel (hexane) afforded 0.22 g (84%, E=Z ¼
96=4) of pinacol (E)-4-phenyl-1-butenylboronate 7 as a colorless
oil. bp 115 ꢁC (bath temp, 0.9 Torr); IR (neat): 3027, 2978,
2930, 1454, 1398, 1390, 1378, 1363, 1321, 1270, 1216, 1165,
2895, 1260, 1250, 1061, 840, 758, 709, 696 cmꢂ1 1H NMR
;
(CDCl3) ꢀ 0.25 (s, 9H), 4.44 (s, 1H).
A Typical Procedure for an Alkenylsilane Using a Catalytic
Amount of CrCl3[thf]3 [Trimethyl[(E)-4-phenyl-1-butenyl]-
silane (2)]: Under an argon atmosphere, Me3SiCl (1.5 mL, 12
mmol) was added at 25 ꢁC to a suspension of CrCl3[thf]3 (0.15
g, 0.40 mmol), and manganese (0.66 g, 12 mmol) in THF (20
mL). After the mixture was stirred at 25 ꢁC for 30 min, a solution
of 3-phenylpropanal (0.27 g, 2.0 mmol) and Me3SiCHI2 (1, 1.4 g,
4.0 mmol) in THF (10 mL) was added at 25 ꢁC to the mixture over
a period of 4 h. The color of the mixture gradually turned from gray
to pale brown during the addition. The reaction mixture was poured
into water (50 mL) and the organic layer was extracted with hexane
(3 ꢃ 30 mL). The organic extracts were washed with brine, dried
over anhydrous MgSO4 and concentrated. Purification by column
chromatography on silica gel (hexane) gave trimethyl(4-phenyl-
1-butenyl)silane (2) in 86% yield (0.35 g, E=Z ¼ 94=6) as a color-
less oil. bp 92–94 ꢁC (bath temp, 1.0 Torr); IR (neat): 3086, 3064,
3027, 2954, 2898, 2856, 1616, 1497, 1454, 1247, 989, 866, 838,
1146, 973, 850 cmꢂ1 1H NMR (CDCl3) ꢀ 1.27 (s, 12H), 2.45–
;
2.50 (m, 2H), 2.72–2.76 (t, J ¼ 7:9 Hz, 2H), 5.50 (dt, J ¼ 18:0,
1.5 Hz, 1H), 6.70 (dt, J ¼ 18:0, 6.3 Hz, 1H), 7.16–7.33 (m, 5H);
13C NMR (CDCl3) ꢀ 24.7, 34.5, 37.4, 83.0, 125.8, 128.3, 141.7,
153.3 Anal. Calcd for C16H23BO2: C, 74.44; H, 8.98%. Found:
C, 74.28; H, 8.94%.
Pinacol (E)-2-Cyclohexylethenylboronate:18 bp 90 ꢁC (bath
temp, 1.7 Torr); IR (neat): 2978, 2926, 2852, 1636, 1397, 1389,
1371, 1349, 1321, 1147, 998, 971 cmꢂ1 1H NMR (CDCl3) ꢀ
;
1.04–1.19 (m, 4H), 1.27 (s, 12H), 1.62–1.67 (m, 2H), 1.70–1.78
(m, 4H), 1.90–2.12 (m, 1H), 5.35 (dd, J ¼ 18:1, 1.2 Hz, 1H),
6.57 (dd, J ¼ 18:1, 6.2 Hz, 1H); 13C NMR (CDCl3) ꢀ 24.7, 25.9,
26.1, 31.8, 43.2, 82.9, 159.7.
Pinacol (E)-2-Phenylethenylboronate:19
2978, 2930, 1625, 1577, 1495, 1450, 1387, 1353, 1325, 1272,
1211, 1145, 998, 970, 852 cmꢂ1 1H NMR (CDCl3) ꢀ 1.32 (s,
IR (neat): 3026,
729, 698 cmꢂ1
;
1H NMR (CDCl3) ꢀ 0.04 (s, 9H), 2.42 (q, J ¼
;
7:2 Hz, 2H), 2.71 (t, J ¼ 7:2 Hz, 2H), 5.67 (dd, J ¼ 18:6, 1.5
Hz, 1H), 6.08 (dt, J ¼ 18:6, 6.0 Hz, 1H), 7.17–7.33 (m, 5H);
13C NMR (CDCl3) ꢀ ꢂ1:2, 35.2, 38.5, 125.7, 128.2, 128.3,
130.4, 142.0, 146.1. Anal. Calcd for C13H20Si: C, 76.40; H,
9.86%. Found: C, 76.67; H, 9.81%.
[(E)-2-Cyclohexylethenyl]trimethylsilane:16 bp 71–74 ꢁC
(bath temp, 4 Torr); IR (neat): 2952, 2922, 2848, 1614, 1449,
1247, 988, 863, 836 cmꢂ1 1H NMR (CDCl3) ꢀ 0.00 (s, 9H),
;
0.86–2.00 (m, 11H), 5.55 (dd, J ¼ 18:8, 1.5 Hz, 1H), 5.96 (dd,
J ¼ 18:8, 6.0 Hz, 1H); 13C NMR (CDCl3) ꢀ ꢂ1:1, 26.1, 26.2,
32.4, 43.8, 126.1, 152.8. HRMS (EIþ) Calcd for C11H22Si: Mþ
182.1492. Found: m=z 182.1472.
Trimethyl[(E)-2-phenylethenyl]silane:16,17
(bath temp, 0.7 Torr); IR (neat): 2955, 1606, 1574, 1494, 1447,
1247, 988, 867, 843 cmꢂ1 1H NMR (CDCl3) ꢀ 0.15 (s, 9H),
6.48 (d, J ¼ 19:2 Hz, 1H), 6.87 (d, J ¼ 19:2 Hz, 1H), 7.23–7.45
(m, 5H); 13C NMR (CDCl3) ꢀ ꢂ1:2, 126.3, 127.9, 128.5, 129.5,
138.3, 143.5.
12H), 6.17 (d, J ¼ 18:3 Hz, 1H), 7.26–7.50 (m, 6H); 13C NMR
(CDCl3) ꢀ 24.7, 83.2, 127.0, 128.5, 128.8, 137.3, 149.4.
Pinacol (E)-3,3-Dimethyl-1-butenylboronate:20 bp 75 ꢁC
(bath temp, 2.0 Torr); IR (neat): 2978, 2962, 2932, 1634, 1396,
1387, 1379, 1365, 1348, 1321, 1265, 1165, 1147, 1001, 971, 851
cmꢂ1; 1H NMR (CDCl3) ꢀ 1.04 (s, 9H), 1.27 (s, 12H), 5.35 (d, J ¼
18:3 Hz, 1H), 6.64 (d, J ¼ 18:3 Hz, 1H); 13C NMR (CDCl3) ꢀ 24.7,
28.7, 34.9, 82.9, 164.3.
ꢁ
Pinacol (E)-11-Oxo-1-dodecenylboronate: bp 110 C (bath
temp, 2.5 Torr); IR (neat): 2978, 2928, 2855, 1718, 1638, 1421,
1398, 1390, 1363, 1320, 1165, 1146, 971, 850 cmꢂ1 1H NMR
;
(CDCl3) ꢀ 1.19–1.40 (m, 22H), 1.53–1.61 (m, 2H), 2.11–2.16
(m, 2H), 2.16 (s, 3H), 2.41 (t, J ¼ 7:5 Hz, 2H), 5.42 (d, J ¼ 18:0
Hz, 1H), 6.62 (dt, J ¼ 18:0, 6.6 Hz, 1H); 13C NMR (CDCl3) ꢀ
23.8, 24.7, 25.6, 28.1, 29.1, 29.2, 29.8, 35.7, 43.7, 67.9, 82.9,
154.7, 209.3. Anal. Calcd for C18H33BO3: C, 70.13; H, 10.79%.
Found: C, 69.85; H, 10.65%.
bp 64–67 ꢁC
;
ꢁ
Trimethyl[(E)-11-oxo-1-dodecenyl]silane: bp 105 C (bath
Financial support from the Ministry of Education, Culture,
Sports, Science and Technology is gratefully acknowledged.
temp, 1.5 Torr); IR (neat): 3444, 3062, 3026, 2932, 2869, 2835,
1600, 1494, 1453, 1187, 1024, 903, 721, 704, 640 cmꢂ1; 1H NMR
(CDCl3) ꢀ 0.03 (s, 9H), 1.27 (s, 10H), 1.56–1.60 (m, 2H), 2.05–
2.10 (m, 2H), 2.13 (s, 3H), 2.41 (t, J ¼ 7:5 Hz, 2H), 5.60 (d, J ¼
18:6 Hz, 1H), 6.01 (dt, J ¼ 18:6, 6.0 Hz, 1H); 13C NMR (CDCl3)
ꢀ 15.2, 18.8, 23.7, 25.1, 29.7, 40.4, 65.8, 80.8, 127.2, 127.4, 127.9,
129.4, 133.7, 140.6. Anal. Calcd for C15H30OSi: C, 70.79; H,
11.88%. Found: C, 70.52; H, 12.09%.
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