An approach to the construction of aromatic steroids using electrocyclic ring closure

Abstract

Methods for the construction of conjugated trienes in which the central double bond is part of a ring system have been investigated. 2-Chloro-3,4-dihydronaphthalen-1(2H)-one is treated with vinyllithium reagents to give the alcohols (10) which, when heated with ethylmagnesium bromide, rearrange with loss of chloride anions to the α-vinyl ketones (4). The 2-substituted naphthalenone (4f), prepared in this way, is converted into the conjugated triene (7c) by reaction with vinylmagnesium bromide followed by acid-catalysed dehydration. This is cyclised thermally or by irradiation to the cyclohexadienes (13) and (14). By an analogous series of reactions, 5,6,11,12-tetrahydrochrysene (16) is prepared from 2-phenyltetralone.