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

[摘要]：Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [2 + 2] cycloaddn. reactions of alkyl(aryl)ketenes with 2-oxoaldehydes to afford b-lactones, e.g. I, with a-quaternary-b-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.

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