Synthesis of Enantioenriched and Diastereomerically Pure cis-Fused Bicyclic α-Oxy-Substituted γ-Lactones via Epoxidation of Optically Active Homoaldol Products

ABSTRACT By applying the (-)-sparteine-mediated asymmetric deprotonation to 1-O-(2-alkylcycloalk-1-enyl)methyl N,N-diisopropylcarbamates, combined with a lithium-titanium exchange followed by addition to achiral aldehydes, enantioenriched homoaldol products 6 were prepared. Hydroxyl-directed epoxidation resulted in the cleavage of the oxirane ring by the migration of the N,N-diisopropylcarbamoyloxy group to form bicyclic γ-lactols 10 via the corresponding γ-hydroxy aldehydes. After oxidation, diastereomerically pure, penta-substituted γ-lactones 11 were obtained.