Copper(I)-catalyzed transfer of 1-(trimethylsilyl)-1-alkenyl group from boron to tin: Regio- and stereoselective synthesis of (E)-1-(tributylstannyl)-1-(trimethylsilyl)-1-alkenes

Article abstract of DOI:10.1055/s-2001-11418

Stereoselective transfer of 1-(trimethylsilyl)-1-alkenyl group from boron to tin has been realized by a catalytic amount of copper(I) iodide in the presence of aqueous NaOH under extremely mild reaction conditions to provide (E)-1-(tributylstannyl)-1-(trimethylsilyl)-1-alkenes (2) exclusively in good to high yields.

Full text of DOI:10.1055/s-2001-11418

LETTER
403
Copper(I)-Catalyzed Transfer of 1-(Trimethylsilyl)-1-alkenyl Group from
Boron to Tin: Regio- and Stereoselective Synthesis of (E)-1-(Tributylstannyl)-
1-(trimethylsilyl)-1-alkenes
Masayuki Hoshi,* Kazuya Shirakawa, Kiyoshige Takeda
Department of Applied and Environmental Chemistry, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
Fax +81(157)24 7719; E-mail: hoshi@lilac.hokkai.net
Received 11 December 2000
Table 1 Effects of copper compound and its amounta
Abstract: Stereoselective transfer of 1-(trimethylsilyl)-1-alkenyl
group from boron to tin has been realized by a catalytic amount of
Yield of 2a (%)b)
(mol%)
Entry
Cu compound
CuI
copper(I) iodide in the presence of aqueous NaOH under extremely
mild reaction conditions to provide (E)-1-(tributylstannyl)-1-(tri-
methylsilyl)-1-alkenes (2) exclusively in good to high yields.
81
91
86
71
66
53c)
1
2
3
4
5
6
5
10
30
10
10
5
Key words: transfer, copper(I) iodide, boron, tin, 1,1-dimetalloalk-
ene
CuBr
CuCl
Dimetalloalkenes have been increasingly useful in syn-
thetic organic chemistry because in many cases, each met-
al moiety can be substituted separately with different
electrophiles to furnish polysubstituted alkenes in a regio-
and stereoselective manner.1 The synthetic utility of 1-sil-
yl-2-stannylalkene1b,2 and 1-boryl-2-silylalkene,1b,3 both
of which exhibit the different reactivities of these metal
moieties in electrophilic substitution, have been demon-
strated. On the other hand, 1,1-dimetalloalkenes have also
been useful synthons in a variety of carbon-carbon bond
forming reactions.1c Although 1-boryl-1-silylalkene is
readily available via hydroboration of 1-silyl-1-alkyne,4
1-silyl-1-stannylalkene cannot be obtained regioselective-
ly by hydrostannation of 1-silyl-1-alkyne.5 In this paper,
we report a regio- and stereoselective route to (E)-1-
(tributylstannyl)-1-(trimethylsilyl)-1-alkenes (2) using
copper(I) iodide-catalyzed reaction of (Z)-1-(trimethylsil-
yl)-1-alkenyldialkylboranes (1) with tributyltin chloride
in the presence of aq. NaOH.
Cu(acac)2
a Stoichiometric reaction of 1a with n-Bu3SnCl was carried out in the
b
presence of 1 equiv of 2M-NaOH. GLC yields based on 1-(trime-
thylsilyl)-1-hexyne employed. c At the same time, Z-isomer was for-
med in 21% yield.
To elucidate the stereochemistry of 2a, we made use of io-
dinolysis of alkenyltin compounds where the conversion
of carbon-tin bond to carbon-iodine bond proceeds with
retention of configuration.7 Thus, the reaction of 1a with
tributyltin chloride followed by iodinolysis, which pro-
ceeded acceptably even under aqueous conditions, gave
(E)-1-iodo-1-(trimethylsilyl)-1-hexene8 in 63% overall
yield in a one-pot manner from the preparation of dicyclo-
1
hexylborane (Scheme 1). The H NMR spectrum of the
product revealed that in the alkenyl region there is only
one triplet at 7.17 ppm, which is consistent with that re-
ported in the literature.9 This result demonstrates that the
geometry of 2a is E, and thus stereoselective transfer of
1-(trimethylsilyl)-1-hexenyl group from boron to tin has
been accomplished by the present reaction.
The reactions of several types of 1,1b which bear structur-
ally and electronically diverse R2, with tributyltin chloride
were carried out under the conditions using additive and
varying the type of R1 and the amount of aq. NaOH, and
the results are summarized in Table 2. The addition of NaI
(an equivalent amount to tributyltin chloride) to the reac-
tion mixture resulted in a moderate improvement of the
reaction yield (entries 2 and 6); however, there is no clear
indication for the role that NaI plays in the reaction. The
reaction starting from 3-methoxy- or 3-(meth-
oxymethoxy)-1-(trimethylsilyl)-1-propyne gave a mix-
ture of regioisomeric products, respectively. This is due to
a lack of regioselectivity in the hydroboration. The regi-
oselective formation of desired products was thus
We examined the reaction of (Z)-1-(trimethylsilyl)-1-hex-
enyldicyclohexylborane (1a), prepared by hydroboration
of 1-(trimethylsilyl)-1-hexyne with dicyclohexylborane,
with tributyltin chloride and thus found that copper(I) salt
and aq. NaOH were required to perform the desired reac-
tion, transfer of 1-(trimethylsilyl)-1-hexenyl group from
boron to tin. The results carried out under several condi-
tions are shown in Table 1. When 10 mol% of copper(I)
iodide was used, the desired reaction proceeded at 0 °C to
room temperature to form (E)-1-(tributylstannyl)-1-(tri-
methylsilyl)-1-hexene (2a)6 in 91% yield in a stereoselec-
tive manner (entry 2). Copper (I) bromide and chloride
also catalyzed the reaction in a similar manner to give 2a
in moderate yields (entries 4 and 5), respectively, while
copper(II) acetylacetonate-catalyzed reaction gave a mix-
ture of stereoisomers (entry 6). Consequently, copper(I)
iodide was identified as the optimal catalyst for further ex-
ploration.
Synlett 2001 No. 3, 403–405 ISSN 0936-5214 © Thieme Stuttgart · New York

404
M. Hoshi et al.
LETTER
H
H
)2B
n-Bu3Sn
cat. CuI / aq. NaOH
0 °C ~ r.t.
C
C
+
n-Bu3SnCl
C
C
Me3Si
C4H9-n
Me3Si
C4H9-n
(1a)
(2a)
Yield 91% (E >99%)
H
I
I2
C
C
_15 °C
r. t., 1 h
Me3Si
C4H9-n
Yield 63% (E >99%)
Scheme 1
Pd(PPh3)4 (10 mol%)
H
H
n-Bu3Sn
Me3Si
CuCl (5 equiv) LiCl (6 equiv)
C
C
C
C
+
I
DMSO, 60 °C, 24 h
C4H9-n
Me3Si
C4H9-n
(2a)
Yield 93%
Scheme 2
achieved by employing dihexylborane which was pre- might participate in the present reaction, as previously re-
pared by successive reaction of 1-hexene with ported by Liebeskind et al12a,b and Evans et al.12c
BH2Br•SMe2 and LiAlH4.11 Moreover, increasing the
amount of aq. NaOH, the products, 2f and 2g, were ob-
tained in good yields (entries 7 and 8). In all cases listed
10
The synthetic utility of 2 thus prepared has been demon-
strated by the palladium catalyzed cross-coupling reaction
with aromatic halide (Stille reaction) (Scheme 2). The re-
in Table 2, (E)-1-(tributylstannyl)-1-(trimethylsilyl)-1-
action of 2a with iodobenzene in the presence of a catalyt-
alkenes (2) were obtained regio- and stereoselectively, in-
ic amount of Pd2(dba)3 scarcely proceeded under the
dicating that a wide range of 2 can be formed using this
conditions described in the literature.13 The system con-
strategy. Although we have no clear evidence for the reac-
taining Pd(PPh3)4 reported by Corey et al,14 however, suc-
tion mechanism at present, it is likely copper(III) species
cessfully catalyzed the reaction to provide the
corresponding coupling product15 as the sole isomer in
93% yield.
Table 2 Transfer of 1-(trimethylsilyl)-1-alkenyl group from boron
In summary, we have found that copper(I) iodide-cata-
lyzed transfer of 1-(trimethylsilyl)-1-alkenyl group from
boron to tin has enabled the development of the first regio-
and stereoselective synthesis of (E)-1-(tributylstannyl)-1-
(trimethylsilyl)-1-alkenes (2). Products 2 would make
trisubstituted alkenes readily accessible with high ste-
reospecificity. Studies on the mechanism and the synthet-
ic scope of this reaction are now in progress.
to tin catalyzed by copper(I) iodidea
CuI (10 mol%)
n-Bu3SnCl, aq.NaOH
R12B
Me3Si
n-Bu3Sn
H
H
R2
C
C
C
C
R2
0 °C ~ r.t.
Me3Si
(1)
(2)
R2
Product Yield (%)b)
R1
Entry
1
2
3
4
5
6
7
8
n-C4H9
2a
2a
2b
2c
2d
2e
2f
91
97c)
References and Notes
88
t-C4H9
(1) For reviews, see: (a) Ishiyama, T.; Miyaura, N. J. Synth. Org.
Chem. Jpn. 1999, 57, 503. (b) Suginome, M.; Ito, Y. Chem.
Rev. 2000, 100, 3221. (c) Marek, I. Chem. Rev. 2000, 100,
2887.
(2) Mitchell, T. N.; Killing, H.; Dicke, R.; Wickenkamp, R. J.
Chem. Soc., Chem. Commun. 1985, 354. Chenard, B. L.;
Laganis, E. D.; Davidson, F.; RajanBabu, T. V. J. Org. Chem.
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1986, 51, 3561. Mitchell, T. N.; Wickenkamp, R.; Amamria,
A.; Dicke, R.; Schneider, U. J. Org. Chem. 1987, 52, 4868.
(3) Suginome, M.; Nakamura, H.; Ito, Y. Chem. Commun. 1996,
2777. Suginome, M.; Matsuda, T.; Ito, Y. Tetrahedron 1999,
55, 8787.
91
86
94c)
82d)
74e)
ClCH2(CH2)2
CH3OCH2
n-C6H13
2g
CH3OCH2OCH2
Unless otherwise stated, stoichiometric reaction of 1 with n-Bu3SnCl
as carried out in the presence of 1 equiv of 2M-NaOH. b GLC yield
ased on 1-(trimethylsilyl)-1-alkyne employed. c 1 equiv of NaI was
dded. d 2 equiv of 2M-NaOH was used. e 2.5 equiv of 2M-NaOH was
sed.
Synlett 2001, No. 3, 403–405 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Copper(I)-Catalyzed Transfer of 1-(Trimethylsilyl)-1-alkenyl Group
405
(4) Zweifel, G.; Backlund, S. J. J. Am. Chem. Soc. 1977, 99, 3184.
Hassner, A.; Soderquist, J. A. J. Organomet. Chem. 1977,
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Farina, V.; Kapadia, S.; Krishnan, B.; Wang, C.; Liebeskind,
L. S. J. Org. Chem. 1994, 59, 5905.
(14) Han, X.; Stoltz, B. M.; Corey, E. J. J. Am. Chem. Soc. 1999,
121, 7600.
(6) 2a: 1H NMR (CDCl3) 0.12 (s, 9H), 0.8__1.0 (m, 18H),
1.1__1.7 (m, 16H), 2.1__2.35 (m, 2H), 6.48 (t, J = 6.8 Hz, 1H);
13C NMR (CDCl3) 1.54 (Me × 3), 10.54 (CH2 × 3), 13.63
(Me × 3), 14.04, 22.43, 27.36 (CH2 × 3), 29.23 (CH2 × 3),
31.92, 36.56, 141.29 (>C=), 159.05 (=CH-); IR (neat) 2956,
2925, 2854, 1566, 1461, 1377, 1247, 858, 835, 750, 684 cm-1;
MS (EI) m/z 389 (M+ 57, 100%), 387 (M+ 57, 75), 385 (M+
57, 43), 235 (31), 233 (26), 231 (16), 193 (31), 191 (22), 189
(13), 179 (40), 177 (36), 175 (24), 139 (12), 135 (11), 121
(12), 73 (36), 59 (12).
(15) (Z)-1-Phenyl-1-(trimethylsilyl)-1-hexene: 1H NMR (CDCl3)
0.19 (s, 9H), 0.98 (t, J = 6.4 Hz, 3H), 1.3__1.7 (m, 4H),
2.2__2.5 (m, 2H), 6.13 (t, J = 7.5 Hz, 1H), 6.95__7.45 (m, 5H);
13C NMR (CDCl3) 0.77 (Me × 3), 14.04, 22.47, 32.04,
32.16, 125.21 (=CH-), 127.53 (=CH- × 2), 127.69 (=CH- × 2),
142.96 (>C=), 146.83 (=CH-), 147.40 (>C=); IR (neat) 2956,
2925, 2871, 2858, 1600, 1488, 1465, 1458, 1440, 1249, 887,
837, 765, 700, 619 cm-1; HRMS (EI), C15H24Si requires
232.1647, found 232.1671.
(16) Typical experimental procedure: To a stirred solution of 1a
(3 mmol) in THF (12 mL) at 0 °C, copper(I) iodide (0.057 g,
0.3 mmol) and sodium iodide (0.45 g, 3 mmol) were added
under an argon flow. Tributyltin chloride (0.813 mL, 3 mmol)
and 2M NaOH (1.5 mL, 3 mmol) were then added dropwise to
the suspended solution, and the resulting mixture was allowed
to warm gradually to room temperature overnight. The
reaction mixture was treated with 3M NaOH (3 mL) and 30%
H2O2 (1.5 mL) at 0 °C and stirred for 1 h at the same
temperature to decompose the residual organoboron
compound. After removal of THF under reduced pressure, the
resultant mixture was extracted with hexane. The extract was
washed with water to remove cyclohexanol formed by the
above decomposition and dried over anhydrous Na2SO4. The
solvent was removed under reduced pressure, and the crude
product was purified by column chromatography on silicagel
60 silanized (Merck), with CH2Cl2 as eluent, to give product
2a (1.123 g, 84%).
(7) For example, see: Ensley, H. E.; Buescher, R. R.; Lee, K. J.
Org. Chem. 1982, 47, 404. Tolstikov, G. A.; Miftakhov, M. S.;
Danilova, N. A.; Vel’der, Ya. L. Synthesis 1986, 496.
(8) (E)-1-Iodo-1-(trimethylsilyl)-1-hexene: 1H NMR (CDCl3)
0.27 (s, 9H), 0.90 (t, J = 6 Hz, 3H), 1.15__1.55 (m, 4H),
1.95__2.25 (m, 2H), 7.17 (t, J = 7.9 Hz, 1H); 13C NMR
(CDCl3) 1.21 (Me × 3), 13.84, 22.19, 31.35, 34.89, 106.44
(>C=), 156.69 (=CH-); IR (neat) 2956, 2925, 2856, 1587,
1461, 1249, 840, 758, 626 cm-1; MS (EI) m/z 282 (M+, 21%),
185 (38), 139 (44), 73 (100).
(9) Zweifel, G.; Murray, R. E.; On, H. P. J. Org. Chem. 1981, 46,
1292.
(10) Brown, H. C.; Ravindran, N.; Kulkarni, S. U. J. Org. Chem.
1979, 44, 2417.
(11) Brown, H. C.; Kulkarni, S. U. J. Organomet. Chem. 1981,
218, 299.
(12) (a) Allred, G. D.; Liebeskind, L. S. J. Am. Chem. Soc. 1996,
118, 2748. (b) Zhang, S.; Zhang, D.; Liebeskind, L. S, J. Org.
Chem. 1997, 62, 2312. (c) Evans, D. A.; Katz, J. L.; West, T.
R. Tetrahedron Lett. 1998, 39, 2937.
Article Identifier:
1437-2096,E;2001,0,03,0403,0405,ftx,en;Y21200ST.pdf
Synlett 2001, No. 3, 403–405 ISSN 0936-5214 © Thieme Stuttgart · New York