Synthetic studies on terpenoid compounds. Part 27. Total synthesis of calodendrolide

A synthesis of calodendrolide (1) was explored starting from 4,7a-dimethyl-1,4,5,6,7,7a-hexahydro-2H-inden-2-one (4). The synthesis of key aldehyde ester (5) by a route involving derivation of α,β,γ,δ-diepoxy compound (8) and selective removal of the γ,δ-epoxy group failed. The second approach was based on the regio- and stereo-selective epoxidation of derived dienol (9), making use of the orientation effect of the hydroxy group, which successfully gave α,β-epoxidised derivative (10) with correct stereochemistry. Treatment of the key intermediate (5), obtained from compound (10), with 3-lithiofuran afforded (±)-calodendrolide (1) together with its epimer (6).