Diterpenoids. Part XVIII. Synthesis and stereochemistry of 1,2,3,4,4a,9a-hexahydro-1β,4aα-dimethylfluorene-1α,9-dicarboxylic acids

Abstract

A reduced fluorene derivative (III) regarded as a basic skeleton of gibberellins was previously synthesized from (–)-abietic acid (I) by a benzilic acid rearrangement of a diketo-ester (II). The four possible stereoisomers, the 1,2,3,4,4a,9a-hexahydro-1β,4aα-dimethylfluorene-1α,9-dicarboxylic acids (VIII), (IX), (XIV), and (XV), and their esters, (X), (XI), (XII), and (XIII), have been prepared from (III) for the synthesis of the gibberellin skeleton. Their stereochemistry is discussed.