4290
J. Am. Chem. Soc. 1999, 121, 4290-4291
Scheme 1
Palladium-Catalyzed
Dimerization-Carbostannylation of Alkynes:
Synthesis of Highly Conjugated Alkenylstannanes
Eiji Shirakawa,*,† Hiroto Yoshida,‡ Yoshiaki Nakao,‡ and
Tamejiro Hiyama*,‡
Graduate School of Materials Science
Japan AdVanced Institute of Science and Technology
Asahidai, Tatsunokuchi, Ishikawa 923-1292, Japan
Department of Material Chemistry
Graduate School of Engineering, Kyoto UniVersity
Sakyo-ku, Kyoto 606-8501, Japan
ReceiVed January 4, 1999
Carbometalation of alkynes produces cis-substituted alkenyl-
metals and is an extremely useful method for a stereoselective
olefin synthesis.1 Among these, the transition metal-catalyzed
carbostannylation has advantages in view of synthetic utility, since
the resulting alkenylstannanes can be transformed further to vari-
ously substituted ethylenes through cross-coupling reactions.2 We
have already demonstrated that a palladium complex coordinated
by a N-(2-diphenylphosphinobenzylidene)-2-phenylethylamine lig-
and (1) catalyzes syn-addition of alkynylstannanes to alkynes.3
Since then we have been studying activities of palladium catalysts
using various ligands and have found that dimerization-car-
bostannylation of alkynes takes place with alkynyl-, alkenyl-, and
allylstannanes. Herein we report that the reaction provides a con-
venient method to produce highly π-conjugated alkenylstannanes
with three to six covalent bonds being generated in one batch.
Using bis(phenylimino)acenaphthene (2a) in lieu of iminophos-
phine 1 as a ligand, we observed that the palladium-catalyzed
carbostannylation of ethyl propiolate (3a) with tributyl(phenyl-
ethynyl)tin (4a) proceeds smoothly, being accompanied by dim-
erization of the alkyne to give diethyl (1Z,3E)-6-phenyl-1-tri-
butylstannylhexa-1,3-dien-5-yne-1,4-dicarboxylate (5a)4 through
a stereoselective syn-addition (Scheme 1). Typical conditions fol-
low: a reaction of 3a (3 mol) with 4a (1 mol) in toluene in the
presence of a 1:2 mixture of [PdCl(η3-C3H5)]2-2a (5 mol % of
Pd) at 50 °C for 40 min gave 5a in 77% yield as a single isomer.
Solvent and a palladium complex coordinated by a different ligand
were examined and compared in the reaction of 3a with 4a.
Conversion in a period of 1 h is summarized in Table 1. In such
a polar solvent as THF, dioxane, DME, or DMF, the reaction
with the Pd-2a catalyst was slow (entries 1-6). Diimines having
an electron-withdrawing or -donating substituent on Ar did not
accelerate the reaction (entries 8-11). Bulky diimine 2f was tot-
ally ineffective (entry 12). A palladium complex with acyclic di-
imine ligand 2g gave a mixture of 2:1 and 1:1 carbostannylation
products (entry 13). Only a 1:1 carbostannylation product was
obtained with a palladium-1 catalyst as we disclosed before
(entry 14).3 The reaction without any ligand was slow to give
1:1 carbostannylation product 7 (R1 ) Et, R2 ) H, R3 PhC2) in
a low yield (entry 15).
Table 1. Palladium-Catalyzed Dimerization-Carbostannylation of
Ethyl Propiolate (3a) with Tributyl(phenylethynyl)tin (4a)a
entry
ligand (Ar in 2)
solvent
conv. (%)b
prod(s)
1
2
Ph
(2a)
(2a)
(2a)
(2a)
(2a)
(2a)
(2a)
(2b)
(2c)
(2d)
(2e)
(2f)
(2g)
(1)
toluene
THF
89
71
70
70
64
53
<5
80
49
68
89
<5
31
84
20
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a, 7c
7d
Ph
3
Ph
dioxane
CHCl3
DME
4
Ph
5
Ph
6
Ph
DMF
7
Ph
octane
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
8
4-CF3C6H4
3,5-(CF3)2C6H3
4-MeOC6H4
4-MeC6H4
2,6-(i-Pr)2C6H3
9
10
11
12
13
14
15
none
7e
a The reaction was carried out in a solvent (3 mL) at 25 °C using 3a
(1.0 mmol) and 4a (0.34 mmol) for 1 h in the presence of [PdCl(η3-
C3H5)]2 (8.2 µmol) and a ligand (16 µmol). b Determined by 119Sn NMR.
c 5a/7 ) 54/46. d The regioisomer of 7 was also detected (7/isomer )
4/1). e Regioisomer was not detected.
The scope and limitations of the dimerization-carbostannyl-
ation were next examined using various organostannanes and
alkynes (Table 2). Tributyl(hexynyl)tin and tributyl(trimethylsi-
lylethynyl)tin also reacted with 3a with high regioselectivities in
good yields (entries 2 and 3). Alkenylstannanes were more reac-
tive than alkynylstannanes to give the corresponding conjugated
(stannyl)trienes consisting of two regioisomers5 by the reaction
with 3a (entries 4-6). In addition to 3a, dimethyl acetylenedi-
carboxylate (3b) also was applicable to the reaction with these
organostannanes (4a-f), giving alkenylstannanes 5g-l6 in a ster-
eoselective manner (entries 7-12). At least one ester substituent
† Japan Advanced Institute of Science and Technology.
‡ Kyoto University.
(1) For a review on carbometalation, see: Knochel, P. In ComprehensiVe
Organic Synthesis; Trost, B. M., Fleming, I., Semmelhack, M. F., Eds.;
Pergamon Press: New York, 1991; Vol. 4, Chapter 4.4; pp 865-911;
Carbocupration, see: Normant, J. F.; Alexakis, A. Synthesis 1981, 841-870;
Zirconium-catalyzed carboalumination, see: Negishi, E.; Takahashi, T.
Synthesis 1988, 1-19; Nickel-catalyzed carbozincation, see: Stu¨demann, T.;
Knochel, P. Angew. Chem., Int. Ed. Engl. 1997, 36, 93-95.
(2) (a) Pereyre, M.; Quintard, J.-P.; Rahm, A. Tin in Organic Synthesis;
Butterworth: London, 1987. (b) Paquette, L. A. Org. React. 1997, 50, 1-652.
(3) Shirakawa, E.; Yoshida, H.; Kurahashi, T.; Nakao, Y.; Hiyama, T. J.
Am. Chem. Soc. 1998, 120, 2975-2976.
(4) Configuration of 5a was determined by the coupling constants in NMR
shown below. For the coupling constants between an allylic carbon and an
olefinic proton in an enyne, see: Breitmaier, E.; Voelter, W. Carbon-13 NMR
Spectroscopy, 3rd ed.; VCH: New York, 1987; Chapter 3.2. For those between
a tin and an olefinic proton in an alkenylstannane, see: Leusink, A. J.; Budding,
H. A.; Marsman, J. W. J. Organomet. Chem. 1967, 9, 285-294.
(5) Configuration of 5b-f was determined in a mannaer similar to 5a.
Minor products 6d-f were confirmed to be regioisomers by the coupling
constants between olefinic protons and those between a tin and an olefinic
proton. For example, the data of 6d are shown below.
10.1021/ja990008c CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/15/1999