SCHEME 1
Synthesis of 1,1,4,4-Tetrabromo-2-butenes
and Related Compounds via
Desilylation-Bromination of Silylated
1,3-Butadiene Derivatives
Zhenfeng Xi,*,† Xiaozhong Liu,† Jianming Lu,†
Fengyu Bao,†,‡ Hongtao Fan,† Zhiping Li,†,‡ and
Tamotsu Takahashi*,‡
Peking University-Hokkaido University Joint Lab,
College of Chemistry, Peking University,
Beijing 100871, China, and Catalysis Research Center and
Graduate School of Pharmaceutical Sciences,
Hokkaido University, and SORST, Japan Science and
Technology Corporation (JST), Sapporo 001-0021, Japan
Received June 22, 2004
Abstract: The combination of zirconocene-mediated cou-
pling of silylated alkynes with a protonation-desilylation
or bromination-desilylation process afforded otherwise
unavailable butadiene derivatives. When (E,E)-2,3-dialkyl-
1,4-bis(trimethylsilyl)-1,3-butadienes were treated with 3
equiv of Br2 in CH2Cl2, (E)-2,3-dialkyl-1,1,4,4-tetrabromo-
2-butenes were obtained in excellent yields with perfect
stereoselectivity.
tion cannot be applied for the preparation of important
1,3-butadiene derivatives 3, 4, or 5 (Scheme 1), because
treatment of halogenated alkynes or terminal alkyes with
Cp2ZrBu2 (Negishi reagent) generally affords complex
mixtures.
It is known that terminally silylated alkynes undergo
regio- and stereoselective coupling on low valent zir-
conocene species to afford silylated 1,3-butadienes (1, R′
) SiMe3).5 On the other hand, hydrolysis-desilylation
of vinylsilanes using CF3CO2H or NaOMe and halogena-
tion-desilylation of vinylsilanes using halogenation re-
agents are well-documented methods for alkenes and
vinyl halides, respectively.8 Therefore, we combined these
two synthetically useful protocols, trying to prepare
hitherto unknown 1,3-butadiene derivatives 3, 4, or 5.
As listed in Table 1, protonation-desilylation of mono-
or disilylated 1,3-butadienes using CF3CO2H afforded
their corresponding products in excellent yields. Both tri-
or disubstituted 1,3-butadienes could be readily pre-
pared.9 For the synthesis of 3a and 3b,3d,7 direct quench
of the reaction mixtures of zirconacyclopentadienes using
CF3CO2H gave 3a and 3b in similar yields.
Stereodefined substituted 1,3-butadienes and 1,4-
dihalo-1,3-butadienes are synthetically important interme-
diates.1-4 (1-5 in Scheme 1). The zirconocene-mediated
coupling of alkynes provides a convenient method for the
preparation of the all-trans 1,2,3,4-tetrasubstituted 1,3-
butadienes (1) and 1,4-dihalo-1,3-dienes (2, X ) I, Br, or
Cl).5-7 However, this zirconocene-mediated coupling reac-
* To whom correspondence should be addressed. Phone: +81-11-
706-9149. Fax: +81-11-706-9150.
† Peking University.
‡ Hokkaido University.
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10.1021/jo048940f CCC: $27.50 © 2004 American Chemical Society
Published on Web 11/04/2004
J. Org. Chem. 2004, 69, 8547-8549
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