Termination of Biomimetic Cyclizations by the Allylsilane Function. Formation of the Steroid Nucleus in One Step from an Acyclic Polyenic Chain

Article abstract of DOI:10.1021/ja00360a018

The aim of this project was to modify the cyclization substrate 1, which is known to undergo ring closure to give 2a and 2b, in such a way that a five- instead of six-membered ring D is formed, thus resulting in the construction of the complete steroid nucleus.The substrate 5 was first prepared as shown in Scheme I, but it gave a very complicated mixture of cyclization products.However, the substrate 18, which was obtained as depicted in Scheme II, afforded the tetracyclic products 24 and 25 in >34percent yield.The steroidal constitution of the nucleus of these products was established by their transformation into the known 17α- and 17β-vinylandrostenones 36, which are convertible into progesterone.