Equilibrium between a vinylogous ylide and a phosphonium dienolate zwitterion: vinylogous Wittig olefination versus vinylogous aldol-type reaction

TETRAHEDRON

卷:66

Article

Khong, San N.¹  Tran, Yang S.¹  Kwon, Ohyun¹ 

[1] Univ Calif Los Angeles, Dept Chem & Biochem, Los Angeles, CA 90095 USA

关键词: Phosphine;    Allenoate;    Phosphonium dienolate;    Vinylogous ylide;    Vinylogous Wittig;    Vinylogous aldol;   

DOI  :  10.1016/j.tet.2010.03.044

来源: Elsevier

【 摘 要 】

This paper describes the equilibrium established between a phosphonium dienolate zwitterion and a vinylogous phosphorus ylide, and their reactions with aldehydes. The reactions between ethyl 2-methyl-2,3-butadienoate and various aldehydes occur through either a phosphonium dienolate or a vinylogous ylide intermediate, depending on the presence/absence of a Lewis acid and the nature of the phosphine. We observed a rare vinylogous Wittig olefination from the reaction between ethyl 2-methyl-2,3-butadienoate and an electron-deficient aromatic aldehyde in the presence of a stoichiometric amount of an electron-deficient triarylphosphine and a catalytic amount of a Lewis acid (e.g., BF(3)center dot Et(2)O). On the other hand, the use of triphenylphosphine, in the absence of a Lewis acid, facilitated vinylogous aldol addition, accompanied by a rare 1,2-aryl phosphorus-to-carbon migration. (C) 2010 Elsevier Ltd. All rights reserved.

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