Abstract
In order to obtain the key intermediates leading to the D-homo cardenolide analogs, the preparation of the C-17a epimeric D-homo-5α, 14β-pregnan-20-ones (VIII, IX) has been undertaken. Upon catalytic hydrogenation the Δ14, 16-dien-17a-one (IV), derivable from D-homo-5α-androstan-17a-one (I) by repeated unsaturation, provided the desired 14β-steroid (V) as a main product. Introduction of a C2 unit into C-17a was attained by the Grignard reaction with ethynylmagnesium bromide, followed by hydration with mercury resin to yield D-homo-5α, 14β, 17a-pregn-17-en-20-one (VII). Subsequent hydrogenation over palladium-on-charcoal afforded IX and VIII in a ratio of ca. 5 to 1. Configurational assignment of the side chain in IX was accomplished by transforming the 20-oxime (XIV) into the 17aα-acetamido derivative (XV) by the Beckmann rearrangement.
