Palladium-catalyzed intramolecular bis-silylation of propargylic alcohols: A new stereospecific access to chiral allenylsilanes

Full text of DOI:10.1021/jo960778w

4884
J . Org. Chem. 1996, 61, 4884-4885
starting propargylic alcohol was nearly completely trans-
ferred to the homopropargylic alcohol.
P a lla d iu m -Ca ta lyzed In tr a m olecu la r
Bis-Silyla tion of P r op a r gylic Alcoh ols: A
New Ster eosp ecific Access to Ch ir a l
Allen ylsila n es
A toluene solution of disilanyl ether 1a derived from
3-decyn-2-ol was heated in the presence of the palladium
catalyst prepared from Pd(acac)2 (2 mol %) and 1,1,3,3-
tetramethylbutyl isocyanide (8 mol %) under nitrogen.
Intramolecular addition of the Si-Si bond across the
carbon-carbon triple bond took place in refluxing toluene
for 1 h to give four-membered product 2a nearly quan-
titatively. Though the formation of 2a could be confirmed
by 1H and 13C NMR analyses of the reaction mixture,
instability of 2a prevented its isolation by chromatogra-
phy on silica gel or by distillation. The Si-O bond in
the strained four-membered ring of 2a was readily
cleaved by Grignard reagent at -78 °C to give a ring-
opening product 3 (eq 2).7 Cyclic 2a also underwent
Michinori Suginome, Akira Matsumoto, and
Yoshihiko Ito*
Department of Synthetic Chemistry and Biological
Chemistry, Graduate School of Engineering,
Kyoto University, Kyoto 606-01, J apan
Received April 30, 1996
Organic silicon compounds now play indispensable
roles in organic synthesis. Hence, development of the
methodologies for the stereoselective synthesis of orga-
nosilicon compounds has been highly desired from the
viewpoint of synthetic organic chemistry.1
We have developed bis-silylation of carbon-carbon
multiple bonds on the basis of the activation of the Si-
Si bonds by a palladium-tert-alkyl isocyanide catalyst.2,3
Very recently, we reported a new synthesis of highly
enantioenriched (E)-allylsilanes from chiral allylic alco-
hols with nearly complete overall 1,3-transfer of the
chirality.4 The new synthesis involved diastereoselective
intramolecular bis-silylation of carbon-carbon double
bonds and subsequent Peterson-type syn-elimination. In
this paper, we describe a new synthesis of allenylsilanes,
which are useful for the synthesis of heterocyclic com-
pounds5 as well as homopropargylic alcohols,6 through
intramolecular bis-silylation of propargylic alcohols cata-
lyzed by the palladium-isocyanide catalyst.
protiodesilylation at the silicon atom in the ring by an
addition of tetrabutylammonium fluoride (TBAF) to give
alcohol 4 in good yield. For the bis-silylation of 1a , a
catalyst prepared from Pd2(dba)3CHCl3 (dba ) diben-
zylideneacetone) and bicyclic phosphate, P(OCH2)3CEt,8
was also effective, while the use of a tetrakis(triph-
enylphosphine)palladium(0) complex catalyst resulted in
sluggish reaction (6 h, <40% conversion), being ac-
companied by unidentified byproducts.
The combination of the intramolecular cis-addition of
the Si-Si bonds across the carbon-carbon triple bond
and subsequent Peterson-type syn-elimination success-
fully led to the stereospecific synthesis of highly enan-
tioenriched allenylsilane (eq 1). A Lewis acid-promoted
A reaction of disilanyl ether 1b derived from primary
propargylic alcohol afforded eight-membered ring product
5, which may result from intramolecular bis-silylation
followed by dimerization of the resultant four-membered
ring product, in good yield (eq 3).9 Unstrained dimer 5
failed to react with the Grignard reagent under the
conditions employed for the reaction of four-membered
ring 2.
reaction of the optically active allenylsilane thus prepared
with aldehyde proceeded stereoselectively to give ho-
mopropargylic alcohols with high enantiopurity. In the
course of the overall transformation, the chirality of the
(1) (a) Masse, C. E.; Panek, J . S. Chem. Rev. 1995, 95, 1293-1316.
(b) Langkopf, E.; Schinzer, D. Chem. Rev. 1995, 95, 1375-1408. (c)
Fleming, I.; Dunogue´s, J .; Smithers, R. Org. React. 1989, 37, 57-588.
(2) For carbon-carbon double bonds, see: (a) Suginome, M.; Yama-
moto, Y.; Fujii, K.; Ito, Y. J . Am. Chem. Soc. 1995, 117, 9608-9609.
(b) Suginome, M.; Matsumoto, A.; Nagata, K.; Ito, Y. J . Organomet.
Chem. 1995, 499, C1-C3. (c) Murakami, M.; Suginome, M.; Fujimoto,
K.; Nakamura, H.; Andersson, P. G.; Ito, Y. J . Am. Chem. Soc. 1993,
115, 6487-6498. (d) Murakami, M.; Andersson, P. G.; Suginome, M.;
Ito, Y. J . Am. Chem. Soc. 1991, 113, 3987-3988.
(3) For carbon-carbon triple bonds, see: (a) Murakami, M.; Sugi-
nome, M.; Fujimoto, K.; Ito, Y. Angew. Chem., Int. Ed. Engl. 1993, 32,
1473-1475. (b) Murakami, M.; Oike, H.; Sugawara, M.; Suginome, M.;
Ito, Y. Tetrahedron 1993, 49, 3933-3946. (c) Ito, Y.; Suginome, M.;
Murakami, M. J . Org. Chem. 1991, 56, 1948-1951.
Noteworthy is that the four-membered 2a , formed by
the palladium-catalyzed reaction of 1a , was found to be
(4) Suginome, M.; Matsumoto, A.; Ito, Y. J . Am. Chem. Soc. 1996,
118, 3061-3062.
(7) The MeMgBr reaction did not lead to the formation of an
allenylsilane even on warming the reaction mixture at room temper-
ature.
(8) The catalytic system was also reported to be effective for bis-
silylation of carbon-carbon triple bonds. Yamashita, H.; Catellani, M.;
Tanaka, M. Chem. Lett. 1991, 241-244.
(9) Disubstituted alkynes hardly undergo intermolecular bis-sily-
lation under the conditions; see ref 3.
(5) (a) Becker, D. A.; Danheiser, R. L. J . Am. Chem. Soc. 1989, 111,
389-391. (b) Danheiser, R. L.; Kwasigroch, C. A.; Tsai, Y.-M. J . Am.
Chem. Soc. 1985, 107, 7233-7235. (c) Danheiser, R. L.; Carini, D. J .;
Basak, A. J . Am. Chem. Soc. 1981, 103, 1604-1606.
(6) (a) Danheiser, R. L.; Carini, D. J .; Kwasigroch, C. A. J . Org.
Chem. 1986, 51, 3870-3878. (b) Danheiser, R. L.; Carini, D. J . J . Org.
Chem. 1980, 45, 3927-3929.
S0022-3263(96)00778-5 CCC: $12.00 © 1996 American Chemical Society

Communications
J . Org. Chem., Vol. 61, No. 15, 1996 4885
Ta ble 1. On e-P ot Syn th esis of Allen ylsila n es 6 fr om 1
cessfully achieved (eq 5). Disilanyl ether (R)-1a with
entry
R
SiR′2R′′
6 (yield, %)
1a
2a
3b
4a
5b
6b
Me
Me
Me
c-hex
c-hex
Ph
SiMe2Ph
SiMe2Bu-t
SiMe3
SiMe2Ph
SiMe3
6a (86)
6c (95)
6d (79)
6e (81)
6f (85)
6g (94)
SiMe2Ph
a
Addition of n-BuLi was carried out at 0 °C after toluene was
b
replaced by THF. Addition of n-BuLi at -78 °C in toluene was
followed by addition of THF.
transformed to allenylsilane 6a in high yield by treat-
ment with n-BuLi in THF (eq 4; Table 1, entry 1). The
96.7% ee was reacted according to the procedure de-
scribed above to give allenylsilanes 6a , which showed
specific rotation of [R]20 ) -13.2 (c ) 1.7, benzene).14
A
D
TiCl4-mediated reaction of the enantioenriched 6a with
cyclohexanecarboxaldehyde under the conditions reported
by Danheiser et al. gave syn-homopropargylic alcohol 7
with high diastereoselectivity (95:5).6 The enantiomeric
excess of 7 was determined to be 93.2% ee,15 indicating
that the formation and subsequent reaction of allenylsi-
lane 6a occurred with >95% stereoselectivity. It is pre-
sumed that allenylsilane 6a with (R) configuration was
formed via two stereospecific processes, i.e., cis-addition
of the Si-Si bond to the carbon-carbon triple bond and
syn-elimination of the silanolate. Probably, subsequent
reaction with the aldehyde occurs with high stereoselec-
tivity at the π-face anti to the silyl group to give (1S,2S)-7
with high enantiomeric excess, though determination of
the absolute configuration of 7 is now underway.
formation of 6a is rationalized by a nucleophilic attack
of n-BuLi onto the ring-silicon atom of 2a followed by
Peterson-type syn-elimination of the silanolate n-BuPh2-
SiO-.10,11 Synthesis of various allenylsilanes was sum-
marized in Table 1.12 In the syntheses of Me3Si deriva-
tives 6d and f, addition of n-BuLi (in hexane) to the THF
solution of 2d and f caused undesired nucleophilic attack
onto the silicon atom of the Me3Si group to lower the
yields of allenylsilanes. This side reaction was sup-
pressed by a slightly modified procedure, in which an
addition of slight excess of n-BuLi (in hexane) was carried
out in toluene followed by dilution with THF at -78 °C.13
Stirring the reaction mixture at 0 °C resulted in selective
elimination of the silanolate to give allenylsilanes, but
the elimination reaction proceeded very sluggishly at -78
°C. According to the modified procedure, allenylsilane
6g with the phenyl group γ to the silicon substituent was
prepared in high yield.
The methodology described herein may make possible
a general preparation of highly enantiomerically enriched
allenylsilanes from optically active propargylic alcohols.16
Su p p or tin g In for m a tion Ava ila ble: Detailed experi-
mental procedures and characterization of the new compounds,
1
including H and 13C spectra of intermediate 2a (7 pages).
J O960778W
(13) This procedure is generally applicable for the synthesis of
allenylsilanes. General procedure: To a catalyst prepared from Pd-
(acac)2 (2.5 mg, 8.2 µmol) and 1,1,3,3-tetramethylbutyl isocyanide (4.6
mg, 33 µmol) in toluene (1 mL) was added disilanyl ether 1 (0.41 mmol)
at room temperature. The mixture was stirred under reflux (bath
temperature ) 120 °C) for 1 h and then cooled to -78 °C. A hexane
solution of n-BuLi (0.43 mmol) was added at -78 °C and then stirred
for 20 min. To the mixture was added THF (2 mL) at -78 °C, and the
mixture was allowed to react at 0 °C for 30 min. Extractive workup
with ether followed by column chromatography on silica gel (hexane)
afforded allenylsilanes 6 in the yields indicated in Table 1.
(14) Several attempts at determination of the enantiomeric excess
of the optically active allenylsilane by HPLC or GC with chiral
stationary phase have failed so far.
(15) Enantiomeric excess was determined by HPLC analysis with
a chiral stationary phase column, SUMICHIRAL OA-4500.
Next, synthesis of highly enantioenriched allenylsi-
lanes starting from chiral propargylic alcohols was suc-
(10) Peterson, D. J . J . Org. Chem. 1968, 33, 780-784.
(11) In contrast, similar Peterson elimination of O-lithio-2-(tri-
phenylsilyl)tridecen-3-ol, prepared by the reaction of undecanal with
[R-(triphenylsilyl)vinyl]lithium, was reported not to proceed at room
temperature in ether. Chan, T. H.; Mychajlowskij, W.; Ong, B. S.;
Harpp, D. N. J . Org. Chem. 1978, 43, 1526-1532.
(12) For the convenient synthesis of chlorodisilanes via (diethylami-
no)diphenylsilyllithium, see: (a) Tamao, K.; Kawachi, A.; Nakagawa,
Y.; Ito, Y. J . Organomet. Chem. 1994, 473, 29-34. (b) Tamao, K.;
Kawachi, A.; Ito, Y. J . Am. Chem. Soc. 1992, 114, 3989-3990.
(16) An enantiomerically enriched allenylsilane with an additional
stereogenic center R to the allenyl moiety was synthesized by SN2′
displacement of a chiral alkynyloxirane with an organocuprate. Mar-
shall, J . A.; Tang, Y. J . Org. Chem. 1994, 59, 1457-1464.