Synthesis of (3aS,4S,6aR)-2-Oxo-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-4-yl Acetate, as a Key Synthon in Approaches to (-)-Galiellalactone

The synthesis of bicyclic allyl acetate 2, a promising precursor of (-)-galileolactone 1, is described. The approach is based on the separation of diastereomeric carboxamides obtained by amidation of racemic gem-dichloro-substituted Grieco lactone with (+)-α-methylbenzylamine. Subsequent steps of transformation of an individual diastereomer include reactions of complete reductive dechlorination, construction of an allyl alcohol fragment in the ring part by stereo- and regiospecific bromohydroxylylation with NBS in aqueous THF, and dehydrobromination.