Intramolecular cyclization of 3β-acetoxy-16-picolinylidene-5-androsten-17-one by catalytic hydrogenation

Abstract

Intramolecular cyclization by catalytic hydrogenation of 3β-acetoxy-16-picolinylidene-5-androsten-17-one (IV) (80° and 50-60 atm of hydrogen pressure over Pd/C as catalyst) gives rise to the formation of two cyclic products, namely, 5′,6′,7′,8′-tetrahydro-2′αH-3′αH-9′αH-3β-acetoxy-androst-5-eno [16.17-b]indolizine (VII) and its 9′βH-isomer (VIII), in a total yield of over 80%, the ratio of the two isomers being 3:1. The cyclized products have structures similar to naturally occuring alkaloid solanidine. A mechanism is proposed for the cyclization.