Activated Lactams. VI. The Cycloaddition Reaction of Cyclic Ketene-S, N-acetals with Dimethyl Acetylenedicarboxylate

Abstract

Reaction of ketene-S, N-acetals (1a-c) derived from lactams with dimethyl acetylenedicarboxylate (DMAD) gave the ring-expanded products (3a-c, respectively). On the other hand, similar treatment of N-acetyl ketene-S, N-acetals (5b, c) afforded the [2+2] adducts (6b, c, respectively). Next, the reaction of benzoketene-S, N-acetals (8a-c) with DMAD furnished the ringopened products (13a-c, respectively).