Abstract
New methods of synthesis of the 2-oxo-A-norsteroids (1a, b), starting materials for preparation of 2-oxa-3-oxo-steroids (2a, b) by Baeyer-Villiger reaction, were described. (1) 2-Hydroxymethylene-3-oxosteroids (5a, b) were oxidized with ozone and then with hydrogen peroxide to obtain 2, 3-secosteroid-2, 3-dioic acids (6a, b). By heating with acetic anhydride, the hydroxyl groups in the seco acids (6a, b) were protected as the acetates, and the dicarboxylic groups were changed to acid anhydrides (7a, b) simultaneously. The anhydrides (7a, b) were heated and pyrolysed at 160-180° (bath temperature : 180-240°). When a more higher temperature was used, various side reactions occurred and the yield was minimized. (2) 2, 3-Secosteroid-2, 3-dioic acids (6a, b) were esterified by diazomethane or 1-2% hydrogen chloride in methanol. Dimethyl esters (12a, b) or their acetates (13a, b) were heated with sodium hydride and methanol in toluene to produce 3ξ-carbomethoxy-2-oxo-A-norsteroids (14a, b or 15a, b), which were hydrolyzed by dilute alkali at room temperature. Saponification products (16a, b) were decarboxylated by heating in acetic acid or acetic anhydride to produce 2-oxo-A-norsteroids (1a, b or 8a, b) in excellent yields. The characteristics of the second synthetic route were as follows : purification of the intermediates was not necessary and the purity of the end products was very high.
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