Selective fluorination of (1 S,4 R)-(−)-camphanic acid with sulphur tetrafluoride: preparation of new fluorinated optically active derivatives of camphor and 1,2,2-trimethylcyclopentane

Abstract

Treatment of (1 S,4 R)-(−)-camphanic acid ( 1) with sulphur tetrafluoride affords (1 R,4 S)-(−)-3-oxa-4-(trifluoromethyl)camphor ( 2) as a main product together with small amounts of (1 S,4 R)-camphanoyl fluoride ( 3), (1 R)-3-(trifluoromethyl)camphonenoyl fluoride ( 4) and (1 R)-3,4-dehydrocamphoroyl difluoride ( 5). Reduction of 2 with LiAlH 4 gives the diol, (1 R,3 S)-(+)-3-hydroxy-1,2,2-trimethyl-3-trifluoromethyl-1-cyclopentanemethanol ( 6), which when heated with KHSO 4 readily dehydrates to (1 R,4 S)-(−)-3-oxa-4-(trifluoromethyl)bornane ( 7). Acylation of the diol 6 proceeds regioselectively at the primary hydroxyl group to give exclusively monoacylated derivative 8.