1,3-Dipolar cycloaddition reaction of nitrilimines to a variety of 3-aryl-5
-arylmothylidene-3,5-dihydro-2-phenyl-4N-imidazol-4-ones (3) afforded the c
orresponding 1,3,4,7,8-pentaaryl-1,2,6,8-tetraazaspiro[4,4]-nona-2,6-dien (
4) and not the regio-isomers 2,3,6,8,9-pentaaryl-1,3,7,8-tetraazaspiro[4,4]
nona-1,6-dien-4-ones (5) in high regioselectivity.