Direct stereoselective construction of cyclopropane α-amino acid with contiguous quaternary centers via [4 + 2] annulation reaction

Abstract

A direct diastereoselective synthetic approach to useful cyclopropane α-amino acid was established via base-promoted [4 + 2] annulations between o-aminobenzaldehydes and alkyl 2-aroyl-1-chlorocyclopropanecarboxylates. The annulation reaction proceeded quickly under mildly basic conditions, affording α-aminocyclopropanecarboxylic acid derivatives in moderate to excellent yields with high diastereoselectivities (up to 19 : 1).