Strategies for Heterocyclic Synthesis via Cascade Reactions Based on Ketenimines

The development of highly efficient methodologies for constructing heterocyclic compounds is a major challenge in organic chemistry. This Account presents the recent progresses on cascade strategies for heterocyclic synthesis based on ketenimine intermediates. Three types of cascade reactions for the synthesis of a variety of heterocycles, involving nucleophilic addition to the central carbon of ketenimine, radical addition to the central carbon of ketenimine, and pericyclic reaction of ketenimine, are highlighted in this Account. A brief discussion on the mechanism of copper-­catalyzed azide-alkyne cycloaddition (CuAAC) providing ketenimines is also included.