Unexpected Electrophilic Rearrangements of Amides: A Stereoselective Entry to Challenging Substituted Lactones

摘要

Ever since the original preparation of ketenes and their successful [2+2] cycloaddition with imines reported by Staudinger in 1907, heterocumulenes and their pericyclic reactions have attracted considerable attention. In the latter part of the 20th century, Ghosez and co-workers pioneered the use of keteniminium salts as attractive alternatives to ketenes for cycloadditions with alkenes to give cyclobuta-nones. Indeed, keteniminium salts are more electrophilic than ketenes, show no tendency towards dimerization, and can be prepared readily by treatment of an amide with collidine and triflic anhydride. In spite of their tremendous potential as easily accessible, highly electrophilic reagents, keteniminium salts generated from tertiary amides have hardly been explored beyond the context of [2+2] cycloadditions.