Lipase-Catalyzed Kinetic Resolution Followed by an Intramolecular Diels-Alder Reaction: Enantio- and Diastereoselective Synthesis of an A-Ring Moiety of Furanosteroids.

Furanosteroids are known to exhibit inhibitory activity against phosphatidylinositol-3-kinase and are expected to serve as a basis for the development of therapeutic drugs for various diseases. In this study, a novel protocol is presented for preparation of the furanosteroid A-ring moiety. More specifically, the lipase-catalyzed kinetic resolution of racemic 1-(3-bromofuran-2-yl)-2-chloroethanol with β-substituted (Z)-acrylates and the subsequent intramolecular Diels-Alder reaction of the generated enantiomerically enriched esters were performed to obtain multi-functionalized fused cyclohexenes in excellent enantiomeric ratios (99 : 1 or 98% enantiomeric excess (ee)) and diastereomeric ratios (≥98 : 2). The obtained products possess the appropriate stereochemical structures and absolute configuration for use in the asymmetric synthesis of the A-ring moieties of naturally occurring furanosteroids, including viridin and viridol.