REACTIONS OF ACID ANHYDRIDES .I. REACTIONS OF KETONES WITH TRICHLOROACETIC ANHYDRIDE

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-trichloroacetates 7, 8, 9, 10, 11, 12 and 26. The presence of trichloroacetic acid decreases the rate of the conversion of these ketones to the geminal bis-trichloroacetates. Testosterone acetate (28a), acetophenone (31) and the steroidal dimethylketone 21a, gave, on treatment with trichloroacetic anhydride, the corresponding enol trichloroacetates 30, 33 and 23. Camphor (17) resulted in a rearrangement product, the 1-trichloroacetoxy-camphene 19a. In the presence of trichloroacetic acid, the dimethylketone 21a gave in addition to 23 the aromatization product, 24a and camphor 17 gave in addition to 19a the 2β,4-bis-trichloroacetoxy-bornane 20a. Trichloroacetic anhydride in the presence of p-toluenesulphonic acid converted ketones 1, 3, 5a and 6a, as well as the geminal bis-trichloroacetates 7,9,11 and 12, to the corresponding enol trichloroacetates 13, 14, 15 and 16. The spectral properties of the geminal bis-trichloroacetates and enol trichloroacetates are discussed. The reactivities of the various ketones towards trichloroacetic anhydride were compared, and the mechanism of formation of gem diesters and enol esters is proposed. It is suggested that the gem diesters are invariably intermediates in the conversion of the ketones to the enol esters. © 1969.