SYNTHESIS OF GEM-DIFLUORO DERIVATES OF NATURAL-PRODUCTS BY THE REACTION OF KETONES WITH DIETHYLAMINOSULFUR TRIFLUORIDE

The preparation of gem-difluoro compounds, including 12,12-difluoro- octadecanoic acid, 7,7-difluorohexadecanoic acid, ent-7,7-difluorokauran-19-ol (8), and 2,2,7-trifluoro-10β-methoxycarbonyl-1β,8-dimethylgibban- 1α,4aα-carbolactones (18) and (19), is described. Each synthesis involved fluorination of the appropriate ketone with diethylaminosulphur trifluoride, and the reaction conditions required varied from 6 h at 0°C for the gibberellin derivatives (14) and (15) to 7 d at 115°C for methyl 12-oxo-octadecanoate. gem-Difluorides are usually stable to alkali, but in the fluorogibberellins (18) and (19) the 2,2-difluoro-groups were readily hydrolysed to the corresponding 2-ketones.