Molecular Design by Cycloaddition Reactions. VII. Facile Thermal Isomerization in the Reaction of Isopyrazole with Diphenylcyclopropenone

Abstract

Combination of the diazadiene system with three carbon dienophile in the Diels-Alder reaction would provide a synthesis of seven-membered diazaheterocycles. The reaction of 3,6-disubstituted-1,2,4,5-tetrazines with cyclopropene provides a useful route to 2,5-disubstituted-3,4-diazanorcaradienes and 5H-1, 2-diazepines.² However, in the extensive literature on the Diels-Alder reaction, there are only a few examples of cycloadditions with the azadienes as the 4e components.³

We have examined the reaction of isopyrazole with diphenylcyclo-propenone in the hope of obtaining a convenient synthetic route to the medium-size unsaturated heterocycles. Recently, the reactions of the 4,4-disubstituted isopyrazoles have been indicated to react only with cyclobutadiene⁴ and 4-phenyl-1,2,4-triazoline-3,5-dione as one of the most potent dienophiles.⁵