THE N-ACYL-ALPHA-CYANO-1-AZADIENES - REMARKABLY REACTIVE HETERODIENES IN THE DIELS-ALDER REACTION

A method for the prepartion of the N-acyl-a-cyano- 1-azadienes has been developed and their Diels-Alder reactions have been studied. The intramolecular Diels-Alder reaction of these dienes with unactivated dienophiles occurs readily with a high preference for the exo (anti) reaction pathway. The JV-acyl-a-cyano-l-azadienes are relatively stable allowing for their isolation and an investigation of their intermolecular Diels-Alder reactions. The azadiene 6 reacted with a range of dienophiles such as, ethyl vinyl ether, styrene, 1-hexene, and methyl acrylate. The reaction of 6 with cis- and trans-1-phenylpropene gave different products which was not consistent with a two-step reaction involving a common intermediate. The reactivity, regiochemistry, and stereochemistry of these reactions is interpreted in terms of a concerted mechanism with a transition state possessing a high degree of diradical character. © 1990, American Chemical Society. All rights reserved.