Steroidal N-nitroamines. Part 1. Denitroamination of steroidal 4β-, 6β-, 7α-, and 7β-nitroamines

Abstract

The α-hydroxy-nitroamines 6β-nitroamino-5α-cholestane-3β,5α-diol (26) and 6β- and 4β-nitroamino-5α-cholestan-5α-ol (27) and (30) have been prepared by reactions of cholest-5-en-3β-yl formate, cholest-5-ene, and cholest-4-ene with nitrous acid and boron trifluoride–ether complex, and subsequent treatment with sodium borohydride. The nitroimines (12) and (25), obtained by nitrosation of the corresponding oximes, undergo similar reduction to yield 6β-nitroamino-5α-cholestan-3β-yl acetate (32) and the 7β- and 7α-nitroaminocholest-5-en-3β-yl acetates (36) and (38). The results of denitroamination reactions of these nitroamines, performed with acetic anhydride and pyridine, are consistent with a mechanism involving a nitrous oxide-separated ion-pair intermediate (6). The nitroamines (26), (27), and (30) gave the corresponding 5α- and 4α-oxirans (28), (29), and (31) by intramolecular nucleophilic substitution. The nitroamino (32) yields, by a hydrogen β-elimination, the acetyl derivatives of cholest-4-en-3β-ol (33), cholest-5-en-3β-ol (34), and cholest-6-en-3β-ol (35). The acetates of cholest-5-ene-3β,7β-diol (37) and cholest-5-ene-3β,7α-diol (39) were obtained from the 7β- and 7α-nitroamines (36) and (38) through substitution by a counter-ion, a total retention of configuration for the 7α-nitroamine and 14% inversion for the 7β-isomer being observed.