Palladium-catalyzed bismetallative cyclization of enynes

Article abstract of DOI:10.1021/om000979x

Enynes were reacted with Me₃SiSnBu₃ in the presence of Pd₂dba₃·CHCl₃ or Pd(OH)₂ on charcoal to give cyclized products containing a vinylsilane moiety and a homoallyltin moiety in good yield.

Full text of DOI:10.1021/om000979x

Organometallics 2001, 20, 1907-1909
1907
P a lla d iu m -Ca ta lyzed Bism eta lla tive Cycliza tion of
En yn es
Miwako Mori,* Tomohiro Hirose, Hideaki Wakamatsu, Noriko Imakuni, and
Yoshihiro Sato
Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, J apan
Received November 17, 2000
Sch em e 1. Bism eta lla tive Cycliza tion of En yn e
Summary: Enynes were reacted with Me3SiSnBu3 in the
presence of Pd2dba3‚CHCl3 or Pd(OH)2 on charcoal to
give cyclized products containing a vinylsilane moiety
and a homoallyltin moiety in good yield.
The addition of a bimetallic reagent to a multiple bond
is of interest because new metal-carbon bonds are
formed. It may be expected that further insertion of
various multiple bonds into these metal-carbon bonds
could occur. We have investigated the reactivity of
compounds having an Si-Sn1a bond or an Si-Zr bond.1b
In this context, we investigated the palladium-catalyzed
bismetallative cyclization of enynes with Me3SiSnBu3,
4. If an enyne is treated with 4 in the presence of a
palladium catalyst,2 insertion of the alkyne part of 1
into the Si-Sn bond would be expected to occur to afford
a cyclized compound, 2 or 2′, which have Si-C and
Sn-C bonds.3 Such products could be converted to
various compounds using reactions of the metal-carbon
bonds.
Sch em e 2. Rea ction of En yn e 1a w ith 4 in th e
P r esen ce of P d (0)
When a THF solution containing equimolar quantities
of enyne 1a and Me3SiSnBu3 was stirred at 50 °C in
the presence of a catalytic amount of Pd(PPh3)4 for 4 h,
a small amount of cyclized product 2a was obtained
(14% yield) along with a bismetalated derivative of the
alkyne, 3a , in 80% yield after the usual workup (Table
1, run 1). The 119Sn NMR spectra of 2a and 3a showed
resonances at -15.7 and -53.2, respectively. Thus, 2a
contains an alkyltin moiety. An NOE experiment indi-
cated that the Z-olefin had been formed (Scheme 2). To
confirm the structure of 2a , destannylation was carried
out by treating it with HI in the presence of [Bu4N]I at
Ta ble 1. Rea ction of 1a w ith 4 in th e P r esen ce of
P d (0)a
yield (%)
run
catalyst
solvent time (h) temp 2a 3a 1a
1
2
3
4
5
6
7
8
9
Pd(PPh3)4
PdCl2(PPh3)2
Pd(OAc)2dppb THF
THF
THF
4
6
5
50 °C 14 80
reflux 48
reflux 20 34
7
Pd(cod)Cl2
THF
THF
THF
DMF
toluene
THF
THF
THF
16
45
16
16
16
114
42
20
rt
rt
rt
rt
rt
rt
rt
rt
30
42
63
10
53
86
88
90
40
15
b
PdCl2
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
Pd/C
(1) Mori, M.; Isono, N.; Wakamatsu, H. Synlett, 1999, 269. (b) Mori,
M.; Kuroda, S.; Dekura, F. J . Am. Chem. Soc. 1999, 121, 5591.
(2) 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, 3667. (c)
Chenard, B. L.; Van Zyl, C. M. J . Org. Chem. 1986, 51, 3561. (d)
Mitchell, T. N.; Wickenkamp, R.; Amamria, A.; Dicke, R.; Schneider,
U. J . Org. Chem. 1987, 52, 4868. (e) Murakami, M.; Morita, Y.; Ito, Y.
J . Chem. Soc., Chem. Commun. 1990, 428. (f) Tsuji, Y.; Obora, Y.; J .
Am. Chem. Soc. 1991, 113, 9368. (g) Obora, Y.; Tsuji, Y.; Asayama,
M.; Kawamura, T. Organometallic 1993, 12, 4697. (h) Obora, Y.; Tsuji,
Y.; Kawamura, T. J . Am. Chem. Soc. 1995, 117, 9814. (i) Beletskaya,
I.; Moberg, C. Chem. Rev. 1999, 99, 3435.
(3) Bismetallative cyclization: See: (a) Obora, Y.; Tsuji, Y. Kakehi,
T.; Kobayashi, M.; Shinkai, Y.; Ebihara, M.; Kawamura, T. J . Chem.
Soc., Perkin Trans. 1 1995, 599. (b) Onozawa, S.-y.; Hatanaka, Y.;
Tanaka, M. Chem. Commun. 1997, 1229. (c) Onozawa, S.-y.; Hatanaka,
Y.; Choi, N.; Tanaka, M. Organometallics 1997, 16, 5389. (d) Suginome,
M.; Matsuda, T.; Ito, Y. Organometallic 1998, 17, 5233. (e) Suginome,
M. Ito, Y. Chem. Rev. 2000, 100, 3221.
10
5
2
10 Pd(OH)2/Cc
11 Pd(OH)2/Cd
a
All reactions were carried out using 3 mol % of Pd catalyst
b
and 1.1 equiv of 4. 6 mol % of PdCl2 and 1.5 equiv of 4 were
used. c 6 mol % of Pd(OH)2 on charcoal and 1.1 equiv of 4 were
d
used. 10 mol % of Pd(OH)2 on charcoal and 1.5 equiv of 4 were
used.
0 °C.4 A three-membered ring compound, 5a , was
obtained in good yield (Scheme 3). Probably, protonation
occurs at the R-position of vinylsilane, and then the
(4) Mori, M.; Watanabe, N.; Kaneta, N.; Shibasaki, M. Chem. Lett.
1991, 1615.
10.1021/om000979x CCC: $20.00 © 2001 American Chemical Society
Publication on Web 04/17/2001

1908 Organometallics, Vol. 20, No. 10, 2001
Communications
Ta ble 2. Bism eta lla tive Cycliza tion of En yn e 1
Sch em e 3. Con fir m a tion of th e Str u ctu r e of 2a
iodide anion attacks at the tin atom to close the three-
membered ring.5 On the basis of these results, the
structure of the cyclized compound is determined to be
2a , not 2a ′.
The reaction was carried out under various conditions
to improve the yield of the desired cyclized product 2a
(Table 1). It was found that the formation of the alkyne
bismetalation product 3a could be suppressed by using
a palladium catalyst in the absence of a phosphine
ligand (runs 1-6). THF was a suitable solvent, and
toluene also can be used (runs 6-8). It is noteworthy
that heterogeneous Pd catalysts, Pd/C or Pd(OH)2/C,6
also afforded the desired product 2a in high yield,
although the reaction time was longer (runs 9-11).
substituent on the CdC bond (Figure 1) under similar
conditions (method A) gave 2i7 in only 7% yield. Bicyclic
heterocycle 2g or 2h was produced stereospecifically
from the corresponding enyne 1g or 1h , respectively.
However, in the reaction of 1g, the alkyne bismeta-
lation product 3g was also obtained, which resulted in
a lower yield of desired product 2g. The reaction rate
of enyne 1j (Figure 1), which has a substituent on the
alkyne, was relatively slow, and the cyclized product 2j
was obtained in only 5% yield. The starting material 1j
was recovered in 76% yield after 46 h (method A).
For the mechanism of this bismetallative cyclization,
two possible pathways can be considered (Scheme 4).
(1) The reaction proceeds by oxidative addition of Me3-
SiSnBu3 to Pd(0) to give Me3SiPdSnBu3 (I)8 followed by
insertion of the alkyne part of 1 into the Si-Pd bond to
F igu r e 1.
Various enynes, 1b-1h , were reacted with Me3-
SiSnBu3 in the presence of Pd2dba3‚CHCl3 (method A)
or Pd(OH)2/C (method B). The results are summarized
in Table 2. In each case, the desired product 2 was
obtained in moderate to good yield. The reaction of
enyne 1e, which has an electron-withdrawing substitu-
ent on the CdC bond, afforded the desired product 2e
in moderate yield, while the reaction of 1i with a methyl
(5) Sugawara, M.; Yoshida, J . Chem. Commun. 1999, 505.
(6) Lautens, M.; Kumanovic, S.; Meyer, C. Angew. Chem., Int. Ed.
Engl. 1996, 35, 1329. (b) Lautens, M.; Ostrovsky, D.; Tao, B. Tetra-
hedron Lett. 1997, 38, 6343. (c) Lautens, M.; Smith, N. D.; Ostrovsky,
D. J . Org. Chem. 1997, 62, 8970.
(7) The cyclized product 2e was obtained as a single diastereomer,
whose stereochemistry has not been determined yet.

Communications
Sch em e 4. P ossible Rea ction Cou r se
Organometallics, Vol. 20, No. 10, 2001 1909
cyclized product 2 and Pd(0) is regenerated. (2) On the
other hand, the possibility of the formation of IV3c
cannot be excluded in this mechanism. Thus, insertion
of the CdC bond into the Sn-Pd bond in II could give
complex IV. Reductive elimination from IV should
afford the same cyclized product 2. At present, it is not
clear which pathway is followed in this reaction. Further
studies are in progress.
Su p p or tin g In for m a tion Ava ila ble: Typical procedure
for bismetallative cyclization of enyne 1a , spectral data for 2a -
1
2h and 5a , and H NMR spectrum of 2a -2h . This material is
available free of charge via the Internet at http://pubs.acs.org.
OM000979X
(8) Ozawa, F.; Sakamoto, Y.; Sagawa, T.; Tanaka, R.; Katayama,
H. Chem. Lett. 1999, 1307. (b) Hada, M.; Tanaka, Y.; Ito, M.;
Murakami, M.; Amii, H.; Ito, Y.; Nakatsuji, H. J . Am. Chem. Soc. 1994,
116, 8754.
(9) Very recently, Pd-catalyzed bismetallative cyclization of diynes
with Me3SiSnBu3 has been reported, see: Gre´au, S.; Radetich B.;
RajanBabu, T. V. J . Am. Chem. Soc. 2000, 122, 8579.
give complex II. Intramolecular insertion of the CdC
bond into the C-Pd bond of II then occurs to give
complex III, and reductive elimination finally affords