An expedient method for the prepn. of diastereomerically and, by extension, even enantiomerically pure vicinal difluoroalkanes is described. The two fluorine atoms are introduced in two consecutive steps: ring opening of an oxirane by addn. of hydrogen fluoride and subsequent treatment of the resulting hydroxy fluoride with diethylaminosulfur trifluorides. Thus, sep. treatment of (E)- and (Z)-RCH:CHR [R = (CH2)4Me] via epoxidn., HF addn, and fluorination, gave dl- or meso-RCHFCHFR, resp. [on SciFinder (R)]