A new synthesis of ring-fused alkylidenecyclobutanes by ring-enlargement reaction of bicyclo[n.1.0]alkylidene derivatives

Bicyclo[n.1.0]alkylidene derivatives (ring-fused alkylidenecyclopropanes) reacted with diazomethane to give spiro-pyrazolines regioselectively. Thermal decomposition of spiro-pyrazolines resulted in ring-enlargement and afforded ring-fused alkylidenecyclobutanes (bicyclo[n.2.0]alkylidene derivatives) in high yields.