Abstract Heating of 6-aryl-1, 5-diazabicyclo [3.1. 0] hexanes in the presence of N- arylmaleimides gives rise to 2, 9-diarylperhydropyrazolo [1, 2-a] pyrrolo [3, 4-c] pyrazole-1, 3- diones. It is presumed that thermal cleavage of the CN bond in the diaziridine fragment of the 6-aryl-1, 5-diazabicyclo [3.1. 0] hexanes results in formation of labile azomethinimines that react with N-arylmaleimides to afford the products of 1, 3-dipolar cycloaddition. The ...