Rearrangements of allene oxide, oxyallyl, and cyclopropanone

A detailed theoretical study of the rearrangement of allene oxide to cyclop ropanone and the racemization of substituted cyclopropanones and the isomer ization of substituted cyclopropanones is presented. The rearrangement of a llene oxide to cyclopropanone was found to proceed in a stepwise fashion in which allene oxide first undergoes conversion to oxyallyl via a newly foun d transition structure with subsequent ring closure of the oxyallyl to cycl opropanone. It is shown that a previously found transition structure is on the pathway that results in the racemization of chiral-substituted cyclopro panones. Anew transition structure was also located that accounts for the p reviously observed conversion of cis-2,3-di-tert-butylcyclopropanone to its trans diastereomer. The discussion is based on the results of DFT and CASS CF methods. IRC calculations were carried out for all transition structures located. Single-point energies were calculated with the CASPT2N, QCISD(T), and UQCISD(T) methods. Good agreement was found between the calculated res ults and those available from experiment.