1,3-DIPOLAR ADDITIONS TO CYCLOPROPENES AND METHYLENECYCLOPROPANE

A series of 1, 3-dipolar addition reactions of phenyl azide, tosyl azide, diazomethane, and methyl diazoacetate with cyclopropenes and methylenecyclopropanes was studied. The cyclopropene reaction products indicate that the initially formed intermediate in all cases is a normal 1, 3-dipolar adduct as in the isolated product 13 from diazomethane addition. For phenyl azide addition and methyl diazoacetate addition, ring cleavage products 15, 20, and 21 are formed. In the phenyl azide addition to methylenecyclopropane, the normal adduct is stable, but it undergoes photochemical conversion to the 2-azaspiropentene 28. This ring system could also be constructed by methoxycarbonylnitrene addition to methylenecyclopropane to give 36. The chemistry of 28 and 36 was investigated. Rates of phenyl azide addition were measured and correlated with ionization potentials for a number of strained olefins to show that about 20-25% of ring strain relief in the addition is felt in lowering the transition-state energy. © 1979, American Chemical Society. All rights reserved.