Diterpene synthesis. Part 2. Acid-catalysed cyclisation of p-methoxyphenylethyltrimethylcyclohexanols

Abstract

The acid-catalysed reactions of two phenylethylcyclohexanols, precursors to tricyclic diterpenoids, are reported. The reaction produced both a bicyclic alkene and a tricyclic molecule; the former was converted into the latter in protic media. Conditions for the formation of the naturally occurring trans A–B ring stereochemistry were defined and the mechanism was explored by the use of a deuterium label. Polyphosphoric acid-catalysed cyclisation produced a more complex mixture.