Radical cyclization strategies to terpenoids; syntheses of (±)-β-cuparenone, (±)-laurene and epilaurenes

Abstract

Radical cyclization of the bromide 8̲, obtained in 5 steps from the ketone 9̲, furnished exclusively 14̲ via̲ 6-endo trig cyclization with out any observable amount of 5-exo trig product 1̲. 5-Exo dig radical cyclizatlon of the bromo acetate 23̲, prepared from 18̲ via̲ the aldehyde 21̲, followed by routine transformations furnished the cyclopentenone 26̲, an immediate precursor to α-cuparenone (2̲). Similarly, total synthesis of laurenes 4̲ and 5̲ was achieved via̲ the 5-exo dig radical cyclization of the xanthate 28̲, obtained from the aldehyde 21̲. Syntheses to title compounds based on 5-exo-dig radical cyclisation, along with two unsuccessful approaches to cuparene, are described.