TRANSFORMED STEROIDS: 132. SYNTHESIS OF NATURAL CHIOGRALACTONE

Article abstract of DOI:10.1007/BF00580553

A seven-stage stereospecific synthesis of natural phytosteroid "chiogralactone" has been effected from readily available 3β,16α-diacetoxypregn-5-en-20-one.The scheme of the synthesis includes Reformatorskii reaction with this 20-ketone, the hydrogenation of the δ-lactone formed to the 21α(CH3) saturated lactone, the opening of the ring and the saponification of the 3-acetoxy group, the conversion of the latter into the 3,16α-ditosylate, and the alkaline treatment of the ditosylate,leading to 3,5α-cyclosteroid with a δ-lactone ring and the α(H) configuration of the C(16) center.This is the key stage of the synthesis.Subsequent transformation - the oxidation of the 6-hydroxy group to a 6-keto group, the opening of the cyclopropane ring, and saponification of the 3-acetoxy group - led to the 23 - 16 lactone of 3β,16β-dihydroxy-6-oxo-24-nor-5α-cholan-23-oic acid, which was identical, according to literature characteristics, with "chiogralactone." Another way of approach to its 3,6-dihydroxy analog was studied on the basis of 5,6α:16,17α-diepoxysteroid.It was shown that both Pd and Pt catalyst hydrogenolysis takes place primarily of the 16,17α-oxide ring.