SODIUM BOROHYDRIDE REDUCTION OF UNSATURATED CONJUGATED 12-KETONES DERIVED FROM CHOLIC ACID

Reduction of methyl 3α,7α-diacetoxy-12-oxochol-9(11 )-enate (II) and methyl 3α-acetoxy-12-oxochola-7,9(11)-dienate (V) with sodium borohydride gave in each case a mixture of epimeric allylic alcohols. These were separated and the hydroxy-configurations at C-12 were established by consideration of molecular rotation differences and characteristic 1H n.m.r. spectra. In the mixture from the 9(11)-en-12-one, the quasi-axial 12α-epimer slightly predominates, whereas in that from the 7,9(11)-dien-12-one the quasi-axial 12α to quasi-equatorial 12β-epimer ratio is about 1:2.