Study of the Wittig reaction of benzyltriphenylphosphonium salt and benzaldehyde via ylide-mediated phase-transfer catalysis - Substituent and solvent effects

被引:34
作者
Hwang, JJ [1 ]
Lin, RL [1 ]
Shieh, RL [1 ]
Jwo, JJ [1 ]
机构
[1] Natl Cheng Kung Univ, Dept Chem, Tainan 701, Taiwan
关键词
Wittig reaction; benzylidine ylides; nonpolar solvents;
D O I
10.1016/S1381-1169(98)00274-X
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The Wittig reaction of benzyltriphenylphosphonium salt and benzaldehyde in two-phase organic solvent/water (NaOH) medium was investigated, focusing on the effects of substituent and organic solvent. The substituents chosen for study include CH3, F, Cl, Br, CH3O, NO2, and CF3. The organic solvents include polar solvents (CHCl3 and CH2Cl2) and nonpolar solvents (n-C6H14, C6H6, and CCl4). It was found that the rate of agitation was insignificant and the reaction of benzylidenetriphenylphosphorane and benzaldehyde in the organic phase is the decisive step for determining the Z/E ratio of the product stilbene. In general, the polar solvents exhibit more favorable Z-selectivity. The Z/E ratio of the product stilbene may change substantially by interchanging the substituents on the benzyl group of phosphorus atom and on the phenyl group of aryl aldehyde. In contrast to the meta- and para-substituted benzaldehydes and the ortho-substituted benzylidene ylides, the ortho-substituted benzaldehydes bearing heteroatom substituent exhibit a pronounced enhancement for the Z-selectivity with the order of effectiveness of substituents being CF3 > (Cl, Br)> CH3O > F > NO2. The concerted asynchronous cycloaddition mechanism involving a four-centered transition state is suggested to be operating in these systems. (C) 1999 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:125 / 139
页数:15
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