Eine neue Methode zum Aufbau der Pregnan‐Seitenkette ausgehend von 16‐Oxo‐androstanen. Über Steroide, 152. Mitteilung

The 20,21‐dioxygenated pregnane side chain has been introduced into the 18‐substituted d,l‐Δ14‐16‐oxo‐androstane derivative I by condensation with dimethyl oxalate. The 16‐oxo group was selectively eliminated by conversion of the 21‐ester IIa into the morpholide Xa, catalytic hydrogenation of the 16‐oxo group as well as the 14, 15‐double bond in the enolacetate XIa, followed by base catalysed elimination of the elements of acetic acid and introduction of a 16, 17‐double bond with or without concomitant hydrolysis of the amide function (to give XIIIb and XIII a respectively). Preliminary experiments towards the transformation of the 20‐oxo‐21‐ester grouping obtained from the corresponding acid to the 20, 21‐ketol side chain are also reported. All reactions were carried out under neutral or alkaline conditions, so that the ketalised oxo‐group in ring A could be preserved throughout the synthesis.