(Z)-2-Methyl-3-(phenylthio) propenoic acid and (E)-N-t-butyl-2-methyl-3-(phenylthio) propenamide produce selectively the corresponding allylic carbanion species, which react with aldehydes and ketones. The same carbanion species are also generated from 2-(phenylthiomethyl)propenoic acid and its N-t-butyl amide.