Abstract:
The cyclisation of 1-(p-methoxyphenylethyl)-2,2,6-trimethylcyclohexanol (7) has been studied with a view to synthesising the podocarpane type tricyclic diterpenoids. Literature reports have claimed that acid catalysed cyclisation of the isomeric alcohol 3-(p-methoxyphenylethyl)-2,4,4-trimethylcyclohexanol (39) gives cis and trans-fused isomeric products in almost equal amounts. A detailed study of the reaction has shown that the earlier reports are incorrect and deuterium labelling of (7) in conjunction with careful analysis of the mass spectrum of the product has revealed new features about the mechanism of the cyclisation reaction.
Routes towards the total synthesis of C-2 functionalised diterpenoids have been sought. Much experimentation has produced a successful route involving condensation of 4-ethylenedioxy-2,2,6-trimethylcyclohexanone (141) with p-methoxyphenylacetylene (89) followed by selective hydrogenation and cyclisation, The exploratory reactions and successful synthesis are discussed.