Synthesis of thiophene‐containing steroid‐like molecules via olefinic cyclization reactions

Ring closure of 2‐methyl‐5‐(2‐thienyl)‐2‐pentene (4a) and 2‐methyl‐5‐(3‐thienyl)‐2‐pentene (4b) to the corresponding 4,5,6,7‐tetrahydrobenzo[b]thiophenes 5a respectively 5b, is described. In order to establish the possibility of the direct synthesis of steroids in which the A‐ring is replaced by thiophene, 2‐[6‐(2‐thienyl)‐(Z)‐3‐hexenyl]‐3‐methyl‐2‐cyclopenten‐1‐ol (9a) and its (3‐thienyl)‐substituted analogue (Z)‐ and (E)‐isomers 9b and 9c respectively, were prepared. The (Z)‐isomers failed to give tetracyclic compounds in contrast to 9c which furnished compound 14 in moderate yield.