Regioselective and stereospecific opening of an oxirane system mediated by trifluoroacetic acid and halide anions. A new direct approach to C3-vicinal halohydrins

Glycidol derivatives bearing ester, ether or silyl functionality upon treatment with trifluoroacetic acid (TFA) in the presence of a halide anion (e.g., Bu4NX; X = Cl, Br or I) at room temperature undergo regioselective and stereospecific opening of the oxirane ring to produce the corresponding C3-vicinal haloalkanols in practically quantitative yields.