Synthetic approaches to the ring system of Nicandra (benzenoid ring D) steroids

Abstract

The androstenolone derivative (5) has been converted into the aromatic ring D steroid (39), with the C/D system of the novel natural steroid Nic-10. The route employs the seco-acid (15) which is cyclised to the D-enone (16). Selective D-aromatisation was ensured by regioselective 16_α-phenylselenenylation [see (37)] and exclusive 1,2-addition of an acetyl anion equivalent gave (38). Oxidation and hydrolysis afforded the desired ketone (39), in which the former C/D angular methyl is incorporated into the new D-ring, as in the likely biosynthesis of Nicandra steroids.