The reactions of saturated and unsaturated ketones with trichloroacetic anhydride both alone and in the presence of trichloroacetic and p-toluenesulphonic acids were studied. Treatment of pentan-3-one (1), cyclobutanone (2), cyclohexanone (3), nor-camphor (4), 17β- acetoxy-5α-androstan-3-one (5a) 17β-acetoxy-5β-androstan-3-one (6a) and cyclohexen-2- one (25) with trichloroacetic anhydride resulted in the corresponding geminal bis- ...