Copper-Catalyzed Multicomponent Reactions: Securing a Catalytic Route to Ketenimine Intermediates and their Reactivities

A new type of Cu-catalyzed multicomponent reaction has been developed relying on the in situ generation of N-sulfonyl- or N-phosphorylketenimine intermediates, which are obtained from the cycloaddition of 1-alkynes and sulfonyl- or phosphoryl azides followed by ring-opening rearrangement of the initially formed copper triazole species. This facile and versatile route to ketenimines has led to develop a range of highly efficient multicomponent reactions by employing diverse nucleophiles such as amines, alcohols, water, pyrroles, and thiolates. Additionally, intramolecular version and cycloadditions of the ketenimines with imines or their derivatives have also been developed on the basis of the same strategy. (This article is dedicated to Professor Bong Rae Cho of Korea University on the occasion of his 60th birthday).