Formal Cycloaddition of Disubstituted Ketenes with 2-Oxoaldehydes Catalyzed by Chiral N-Heterocyclic Carbenes

Chiral N-hetereocyclic carbenes were found to be efficient catalysts for the formal [2 + 2] cycloaddition reactions of alkyl(aryl)ketenes with 2-oxoaldehydes to afford β-lactones with α-quaternary-β-tertiary stereocenters in high yields with good diastereoselectivities and excellent enantioselectivities (up to 99% ee). Both alkyl(aryl)ketenes and diarylketene worked well in this reaction.