Application of a Radical Methodology toward the Synthesis of d,l-5alpha-Pregnanes and Related Steroids: A Stereoselective Radical Cascade Approach.

A stereoselective radical cascade cyclization to 5alpha-pregnanes is presented. Oxidative free radical cyclization of an appropriately substituted chloro cyano ester polyene was used to introduce the all trans stereochemistry in the steroid nucleus. The cyano group was utilized to introduce a C-8beta angular hydrogen, while the chloro ester moiety served as an entry to the geminal hydrogens at C-4.