Reductive ring opening of cis- and trans-2,3-diphenyloxirane: a common intermediate

The reaction of both cis- and trans-2,3-diphenyloxirane (7 and 4, respectively) with an excess of lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 2.5 mol%) in the presence of different carbonyl compounds as electrophiles (Barbier conditions) in THF at temperatures ranging between −80 and −50 °C gives the same organolithium intermediate 5 and consequently, the same 1,3-diols 6. In the case of cis-epoxide an inversion of the configuration at the benzylic carbanionic center can explain the obtained results. Only for the dicyclopropyl ketone derivative (6h) some amount (14%) of the corresponding epimer (6′h) resulting from a process with retention of the configuration of the intermediate is obtained. In representative cases, the structure of the final products (6) was unequivocally determined by X-ray diffraction analysis.