APPROACH TO THE SYNTHESIS OF CANDELABRONE AND SYNTHESIS OF 3,7-DIKETO-12-HYDROXYABIETA-8,11,13-TRIENE

An approach to the synthesis of aromatic diterpenes was tested for its generality. Phenylacetonitriles with increasing substitution on the aromatic ring were prepared and alkylated with geranyl bromide and the resulting dienes subjected to cationic cyclization. The less-substituted examples afforded tricyclic products of the required stereochemistry while the more highly substituted compounds cyclized with reduced yields or not at all. One of the intermediates was used to synthesize nimosone (3,7-diketo-12-methoxyabieta-8,11,13-triene), a natural diterpene isolated originally from Chamaecyparis formosensis and recently from Azadirachta indica.