Reaction of alkenes with N-bromosuccinimide and Et3N.3HF produces vic-bromofluoroalkanes in high yields. As long as the addn. to the C:C bond is sterically unhindered, Br and F get attached with very high regioselectivity, the latter occupying the more substituted, carbocation-stabilizing position. 2-Fluoro-1-alkenes give 1-bromo-2,2-difluoroalkanes. The Br may be removed by base-promoted dehydrofluorination to afford fluoro olefins, or by redn. with Bu3SnH, leading to mono- or difluoroalkanes. [on SciFinder (R)]