Semiempirical Calculations in a Search for a Mechanism of 2-Methyl-4-phenylquinoline Formation from 4,4-Diphenyl-3-buten-2-one Oxime Acetate

The known thermal non-catalytic formation of 2-methyl-4-phenylquinoline from 4,4- diphenyl-3-buten-2-one oxime acetate was analyzed by semiempirical MNDO, AM1 and PM3 methods of calculation, assuming the process consists of three steps: thermal disrotatory electrocyclization of the oxime acetate, inversion of the cyclic intermediate on the nitrogen atom and elimination of acetic acid from the inverted intermediate according to Ei mechanism. It appears from PM3 calculations, which led to better results than MNDO or AM1, that the disrotatory electrocyclization is the rate-determining step for the whole synthesis.