The β-keto-ester which is obtained by Dieckmann cyclization of the dimethyl ester (I) of the dicarboxylic acid obtained by oxidative opening of ring A in 5α-cholestan-3-one and related compounds has been shown to have the structure IIa, by its degradation, via the unsaturated acid (Va), to A-nor-5β-cholestan-3-one (VI) and to the dimethyl ester (VIIb). The stereochemistry of compound IIa and of related A-substituted A-nor-5α-cholestanes is discussed. A-nor-5α-Cholestan-1-one (XVIIb) has been synthesized, starting from 5α-cholest-1-en-3-one (XIV).