An easy access to γ-lactone-fused cyclopentanoids

The tricyclic α-keto hemiacetals 3a,b and 8a-d obtained from ruthenium-catalyzed oxidation of tetrahalonorbornyl derivatives possessing a pendant hydroxymethyl group were cleaved using Pb(OAc)₄ or alkaline H₂O₂ to give γ-lactone-fused cyclopentane derivatives 5a,b and 9a-d. The α-keto hemiacetal 3b has also been elaborated to spiroepoxide derivative 25. The stable hydrate 4 formed from ruthenium-catalyzed oxidation of acrolein adduct 10 furnished an intramolecular hemiacetal 11 upon cleavage with Pb(OAc)₄. The α-halo ester moiety in 5a was transformed smoothly in a highly regio- and stereoselective manner to α-hydroxy esters through a lactone-assisted intermediate to furnish 18.