Vinyl carbanions derived from cis-cinnamonitrile-reactions with electrophiles and configurational stability

Abstract

Vinyl carbanions derived from cis-cinnamonitrile 1 were formed by reacting it with lithium diisopropylamide (LDA) as a base in aprotic solvents at low temperatures; reaction with various electrophiles (E) resulted in the corresponding derivatives PhCHC(E)CN. The configurational stability of the vinyl carbanions derived from 1 and the geometry of the reaction products was affected by the solvating properties of the medium. Retention of configuration was achieved in a poor solvating medium-diethyl ether-hexane (4:1). Addition of a crown ether or using THF as solvent resulted in products having trans geometry. The site of deprotonation of cinnamonitrile ( cis and trans) was compared to that of cinnamic esters and discussed. Determination of the geometry of the products was based on their 1H NMR spectra.