Stereoselectivity of the Wittig reaction in two-phase system

Abstract

The Wittig reaction of benzyltriphenylphosphonium chloride with aliphatic and aromatic aldehydes has been investigated, respectively, in two-phase solvent system (dichloromethane / water) in the presence of sodium hydroxide. Both, the effect of the size of aliphatic aldehydes and the effect of substitution on benzaldehyde to the cis/trans ratios have been studied. It has been found that the use of aliphatic aldehydes in Wittig reaction gives higher ratio of trans alkene isomer. However, when aromatic aldehyde is used, the ratio of the cis alkene isomer is found to be higher than that of the trans isomer. In addition, the electronic nature of substituents (electron-donating group versus electron-withdrawing group) causes some changes in the cis/trans ratio of the product stilbene.