| Abstract: | Epimerizations of 16 alpha-chloro- (1a), bromo- (1b), and iodo-3 beta-hydroxy-5-androsten-17-one (1c) by a brief treatment with 0.2 equiv NaOH in aqueous pyridine reached equilibrium between 16 alpha- and 16 beta-halo ketones. 16 alpha-/16 beta-Halo ketone ratios at equilibrium were 1.5 for Cl, 1.25 for Br, and 1.0 for I. Kinetic analysis showed that compounds 1a-c were stereoselectively converted to the corresponding 16 alpha-hydroxy derivative 3 by an SN2 mechanism, in which the order of the apparent reactivity was Br greater than I greater than Cl. The hydrolysis of a number of 16 alpha-bromo-17-ketones and 2 alpha-bromo-3-ketones was carried out. The yields of the corresponding alcohols were found to depend on remote structural features in the steroids. |
