Facile access to optically active ring C aromatic diterpene derivatives from manool. Highly efficient syntheses of (+)-12-methyl-7-oxo-podocarpa-8,11,13-triene-13-carboxylic acid, (+)-13-methyl-7-oxopodocarpa-8,11,13-triene-12-carboxylic acid and (+)-nimbiol

Abstract

The extension of our recently developed strategy using the key intermediate 2, obtainable in two steps (52% overall yield) from manool 1, to the synthesis of naturally occurring ring C aromatic diterpene derivatives provides in three steps (+)-12-methyl-7-oxopodocarpa-8,11,13-triene-13-carboxylic acid 4b and its isomer 6b, and in seven steps (+)-nimbiol 11b, in good overall yields. This synthesis discloses that the structure 4b assigned to margolone isolated from Azadirachta indica A. Juss is incorrect and needs to be reinvestigated.