The N-heterocycliccarbene-catalyzedconjugateUmpolung of differently substituted α,β-unsaturatedaldehydes, e. g. cinnamaldehydes, a-methylcinnamaldehydes, and crotonaldehydes, is described. Coupling of these compounds with a variety of electrophilic aldehydes and ketones results in the selective formation of highly substituted β- and γ-butyrolactones.