Heating of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes in the presence of N-arylm
aleimides gives rise to 2,9-diarylperhydropyrazolo[1,2-a]pyrrolo[3,4-c]pyra
zole-1,3-diones. It is presumed that thermal cleavage of the C-N bond in th
e 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 rate of accumulation
thereof depends only on the character of substituents in the aromatic ring
of the 1,5-diazabicyclo[3.1.0]hexanes and is independent of maleimide. The
thermal isomerization of 6-aryl-1.5-diazabicyclo[3.1.0]hexanes without 1,3
-dipolarophiles yields the corresponding 2-pyrazolines.