Diels–Alder reaction of unsymmetrical dienes with unsymmetrical p-benzoquinones

Abstract

A number of Diels–Alder reactions between 1-phenyl-, 1-p-methoxyphenyl-, and 1-p-nitrophenyl-2,3-dimethylbutadiene and methoxycarbonyl-, 2,6-dimethyl-, 2,5-dimethyl-, 2-methoxy-6-methyl-, 5-methoxy-2-methoxycarbonyl-3-methyl-, and 2-cyano-3,5-dimethyl-p-benzoquinone are reported. The structures of the major products are established and their formation is interpreted on the basis of a transition state having some diradical character.