STUDIES ON PINACOL REARRANGEMENT .V. REARRANGEMENTS OF CIS- AND TRANS-1,2-DIPHENYL-1,2-DITOLYLETHYLENE OXIDES

The intermediate formation of the two epoxides was observed in the perchloric acid-catalysed rearrangement of meso-2,2′-dimethylbenzpinacol (Pmeso) to 2-methylbenzoyl tolyl diphenyl methane (K) Two kinds of epoxides were separated with preparative TLC and the configuration (cis and trans) of these epoxides was inferred in the light of UV, NMR and IR spectra, dipole moment and kinetic data. The rearrangement rates of these epoxides were measured in HClO4-anhydrous acetic acid. Linear correlations of logarithm of the rate constants (log k) with the Hammett acidity function of the medium (H0) were obtained, which supports the A-1 mechanism, together with the large positive values of the entropy of activation. It is shown that the perchloric acid-catalysed rearrangement of meso-2,2′-dimethylbenzpinacol (Pmeso) occurs via such many kinetically distinguishable routes as the following where C and T are cis- and trans-epoxide respectively. The mechanisms of the rearrangements were discussed from the data of kinetics. © 1968.