The significant directing effect of the cyano-group in the reduction of 5-cyano-3-oxo-steroids with complex metal hydrides
The stereochemistry of reduction of 5α- and 5β-cyano-17β-hydroxyandrostan-3-one [(la) and (Va)] and of 5α- and 5β-cyano-17β-hydroxyoestran-3-one [(lb) and (Vb)] with lithium tri-t-butoxyaluminium hydride and sodium borohydride has been investigated. Several earlier stereochemical assignments for the resulting 5-cyano-3α- and 3β-alcohols proved incorrect. In almost every case, formation of the axial alcohol is predominant, this predominance being greater with lithium tri-t-butoxyaluminium hydride in tetrahydrofuran than with sodium borohydride in ethanol. This significant directing effect of the 5-cyano-group is conspicuous and can be accounted for in terms of both steric and polar factors.