cyclopropenes 10 to form tetracyclic azocompounds 12. Photolysis of these compounds, with accompanying loss of nitrogen, affords homotropilidenes (bicyclo[5.1.0]octa-2,5-dienes) 13−26. Substituents at various positions of the homotropilidene skeleton have been observed to exert significant influences on the Cope rearrangement rate and, in cases of unsymmetrically substituted homotropilidenes, on the