DFT Calculations and Synthesis Reveal: Key Intermediates, Omitted Mechanisms, and Unsymmetrical Bimane Products

Theoretical and experimental mixed approaches are complementary and valuable. Our DFT calculations support the mechanism suggested by Kosower, adding to it a key diaziridine intermediate that determines the relative product distribution of this reaction. Our results are consistent with the formation of the diazoketene intermediate as the rate-limiting step. Based on curve fittings, first or second-order kinetics cannot be ruled out. This may indicate that more than one mechanism is simultaneously at play in this transformation. This unexpected outcome led us to study an alternative cyclopropenone intermediate. Although cyclopropenone is not likely to be formed under thermal conditions, adding it to the reaction mixture results in bimane structures. The most staggering finding from this investigation was the unanticipated generation of the unsymmetrical anti-(Me,Me)(Ph,Ph)bimane. The optimization of this route towards unsymmetrical bimanes will require additional investigation. We studied the mechanism behind the formation of fluorescent syn-bimane. This work combines theoretical and experimental approaches. Our computational study supports Kosower's mechanism while introducing a crucial diaziridine intermediate. Our results suggest the rate-limiting step is the formation of a diazoketene. The reaction of 4,5-dimethyl-2,3-diazacyclopentadienone with diphenylcyclopropenone produced the unexpected unsymmetrical anti-(Me,Me)(Ph,Ph)bimane.image