Tandem cyclisations involving α-ketenyl alkyl radicals. New syntheses of the natural triquinanes pentalenene and modhephene

Abstract

New synthetic approaches to the angular and propellane sesquiterpene triquinanes (±)-pentalenene 2 and (±)-modhephene 3, respectively, are described. The syntheses are based on tandem cyclisations involving α-ketene alkyl radical intermediates produced from α,β-unsaturated acyl radical species, as highlighted in Schemes 2 and 4.