Anatomy of ene and Diels–Alder reactions between cyclohexadienes and azodicarboxylates

Abstract

In contrast with other (C ⋯ H ⋯ N) hydrogen transfers, the high-pressure kinetics of the ene reaction between cyclohexa-1,4-diene and diethyl azodicarboxylate show a concerted transition state. The discrepancy is assigned to the enhanced rigidity of the cyclohexadiene molecule with orthogonal hydrogen transfer to the nitrogen atom. Cyclohexa-1,3-diene reacts with diethyl azodicarboxylate according to a concerted Diels–Alder reaction.