Reaction of Trifluoromethyl Ketones. VI. Synthesis of Trifluorinated Analogues of Monoterpenes

The ene reaction product of trifluoroacetone with cyclohexene, 3-(2, 2, 2-trifluoro-1-hydroxy-1-methylethyl)-cyclohexene (1), was converted to trifluorinated analogues of p- and m-menthane derivatives. For introduction of a functional group at suitable positions of the cyclohexene ring, oxidation of 1 was carried out to give 1-(2, 2, 2-trifluoro-1-hydroxy-1-methylethyl)-2-cyclohexen-1-ol (2), 4-(2, 2, 2-trifluoro-1-hydroxy-1-methylethyl)-2-cyclohexen-1-one (3) and 3-(2, 2, 2-trifluoro-1-hydroxy-1-methylethyl)-2-cyclohexen-1-one (4). Selenium dioxide gave only a small amount of 2. The best oxidizing reagent among those examined was tert-butyl hydroperoxide with chromium trioxide or chromium hexacarbonyl as a catalyst. In the presence of basic compounds such as pyridine or dimethylpyrazole, chromium trioxide gave a larger amount of 4 than 3, while in the presence of acetic acid, 3 was formed preferentially though the total yield was very low. Oxidation of 1 with tert-butyl hydroperoxide catalyzed by chromium hexacarbonyl gave 3 in excess over 4 in satisfactory yields. Treatment of the carbonyl compounds (3 or 4) with methylmagnesium iodide gave a p- or m-menthane skeleton with fluorine substituents, and these products were converted to some fluorine analogues of monoterpenes.