Biomimetic total synthesis of steroids IV. Stereoselective synthesis of 15α‐methyl‐19‐norsteroids

The cationic cyclization of 2‐[6‐(m‐methoxyphenyl)‐(E)‐3‐hexenyl]‐3,5‐dimethyl‐2‐cyclopentenol (3) was investigated. Exclusive formation of 1‐ and 3‐methoxy‐15α,17‐dimethyl‐1,3,5(10), 13(17)‐gonatetraene (4 and 5) was observed, indicating complete stereoselectivity in the cyclization process. Compound 4 was converted into dl‐15α‐methylestrone methyl ether (7) and hence into dl‐15α‐methylestradiol 3‐methyl ether (8). The structure of these hitherto unknown compounds was proved by independent syntheses.