Ring expansion and contraction of a two-carbon bridged spiropentane

The reactions of tricyclo[4.1.0.0(1,3)]heptan-4-one (5) and two related systems with diazomethane and m-CPBA were examined in order to determine the relative reactivity and migratory aptitudes for the three compounds. The reactions of 5 with diazomethane and m-CPBA yielded new derivatives of the tricyclo[5.1.0.0(1,3)]octane ring system that showed that migration of cyclopropylcarbinyl is favored over cyclopropyl migration in this system. Photolysis of 5-diazotricyclo[4.1.0.0(1,3)]heptan-4-one (23) in methanol and dimethylamine did not lead to ring contraction to the tricyclo[3.1.0.0(1,3)]hexane ring system, but an interesting product was derived from an unusual rearrangement process in the photolysis in dimethylamine. Matrix photolysis of 23 at 15 K gave a decrease in the diazo band at 2085 cm(-1) and the appearance of a new band at 2117 cm(-1), which is a normal position expected for a small-ring ketene such as cyclopropylketene. Thus, matrix photolysis appears to have yielded a derivative of the previously unknown tricyclo[3.1.0.0(1,3)]hexane ring system. The lithium enolate of 5 was characterized by NMR spectroscopy at -80 degrees C and was found to rearrange to m-cresol at -65 degrees C. The geometries of the bridged spiropentanes of this work were optimized at the MP2(frozen core)/6-31G* level of theory, and group equivalent values were derived in order to calculate the heats of formation for these compounds using the calculated energies.