The Lewis-acid catalyzed rearrangement of parent trans-stilbene oxide 1 was studied with M(OTf)(3)/DCM and M(OTf)(3)/[BMIM][BF4] (M = Bi, Al, Ga, Sc, and Yb; [BMIM] = butylmethylimidazolium) and Zn(NTf2)(2), and with Bi(OTf)(3)/[BMIM][X] (X = NTf2, OTf, PF6, and BF4), employing 5 mol% of catalyst. Selective formation of 2,2-dipheylacetaldehyde 2 (phenyl migration product) was observed in all cases, with Bi(OTf)(3) proving most efficient. The rearrangement of I was also effected in [BMIM][X] (X = NTf2, OTf, PF6, and BF4) without an added catalyst under microwave MW irradiation, and X = PF6 gave the highest yield and selectivity. Efficient and selective rearrangement of 1-2 was also observed with 0.1-0.3 equiv. of [BMIM(SO3H)][OTf] in DCM and in [BMIM][X]. A substituent effect study was performed with a series of singly substituted 1,2-diphenyl oxiranes (with X = OMe, Me, F, CN, and NO2) with 5 mol% Bi(OTf)(3) in DCM and in [BMIM][NTf2]. Notable formation of ketones was observed with the NO2 and CN derivatives. Competing formation of ketones was also observed in [BMIM][PF6] under MW and under Bronsted acid catalysis with [BMIM(SO3H)][OTf] in DCM and in [BMIM][NTf2]. The aryl versus H migration was studied computationally by OFT and MP2 methods and by including solvation effects (IEFPCM). (C) 2014 Elsevier B.V. All rights reserved.