Reactions of carboxyl derivatives of camphor with sulphur tetrafluoride

Treatment of a mixture of endo- and exo-(1R)-3-camphorcarboxylic acid (1) with sulphur tetrafluoride gave initially, (1R)-3-(fluoroformyl)camphor (2) and (1R)-2,2-difluoro-3-(fluoroformyl)bornane (3) but after prolonged reaction time, a mixture of endo- and exo-(1R)-3-(trifluoromethyl)camphor (4) was obtained, albeit in low yield. Carboxylic groups in (1S)-ketopinic and (1R)-trans-isoketopinic acids (5) and (9) were found to be resistant towards SF4 such that at ambient temperature only corresponding acid fluorides (6) and (10) were obtained but under forced conditions fluorination of the carbocyclic ring carbonyl group occurred affording, respectively, (1S)-2,2-difluoro-1-fluoroformyl-7,7-dimethylbicyclo[2,2,1]heptane (7) and (1R)-2,2-difluoro-trans-7-fluoroformyl-1,7-dimethylbicyclo[2,2,1]heptane (11). Hydrolysis of 7 and 11 gave the corresponding acids 8 and 12.