Reaction of diazoalkanes with unsaturated compounds. 10. 1,3-Dipolar cycloaddition of diazocyclopropane to strained cycloalkenes

Abstract

The reaction of diazocyclopropane, generated in situ by alkaline hydrolysis of N-nitroso-N-cyclopropylurea at −20‡ to −40‡C, with the double bond of norbornene hydrocarbons or 3,3-dimethylcyclopropene is a 1,3-dipolar cycloaddition and affords 45–70% yields of thermally stable 1-pyrazolines possessing a spiro-joined cyclopropane fragment. Methylenecyclopropane under the same conditions is a less effective and selective interceptor of diazocyclopropane, forming in ∿ 10% yields not only isomeric 1-pyrazolines but the corresponding product of cyclopropylization, dispiro[2.0.2.1]heptane.