Regiospecific inverse electron demand Diels–Alder reactions of 7-methylcoumarin-4-azadienes

Abstract

Condensation of 7-methylcoumarin-4-carbaldehyde with different anilines affords 7-methylcoumarin-4-azadienes. The 7-methylcoumarin-4-azadienes do not undergo normal electron demand Diels–Alder reaction with N-phenylmaleimide, but react with dihydropyran, dihydrofuran, and styrene via inverse electron demand Diels–Alder reaction in the presence of anhydrous ZnCl₂. The diene involves the azomethine group and the aniline ring. The product is a mixture of two diastereomers in which the major diastereomer has all the hydrogens at the ring junction in cis configuration.