Formal [2+2+1] Synthesis of Tetrasubstituted Furans from Aldehydes, Acetylenedicarboxylates, and Acyl Compounds

Abstract

A combination of 4‐picoline and Ph3P (or nBu3P) efficiently promotes a formal [2+2+1] synthesis of tetrasubstituted furans from aldehydes, acetylenedicarboxylates and acyl compounds under the metal‐free and mild conditions. The present method can be applied not only to acyl chlorides but also trifluoroacetic anhydride as the acyl compounds. These furan products were formed in moderate to excellent yields via O‐acylation of the α,β‐enone intermediates followed by intramolecular Wittig reaction. From the results of control experiments, it was found that 4‐picoline would serve as a promoter in the formation of both α,β‐enones and O‐acyl intermediates as well as a base for capturing of the generated acid.