The reaction of 1-vinyl-4,5-dihydro-1H-benzo[g]indole with C-aryl-N-methylnitrones in the presence of nickel (II) perchlorate proceeds regioselectively to form a mixture of diastereomeric adducts of formal (3+3) cycloaddition, whereas the main products of the reaction with C,N-diarylnitrones are dipyrromethanes.