Highly Stereoselective Radical Cyclization of Haloacetals Controlled by the Acetal Center

A systematic investigation of radical haloacetal cyclizations (Ueno–Stork reaction) where the acetal center is the unique stereogenic element is reported. This highly diastereoselective reaction can be used for the preparation of polysubstituted tetrahydrofurans and γ‐lactones. We report herein the full experimental details of reactions where up to three new chiral centers are created. To demonstrate the potential of this approach, short syntheses of (+)‐eldanolide and of tricyclic acetals related to biologically active lignans have been achieved. Chiral acetal centers allow to control the diastereoselectivity of Ueno–Stork radical cyclizations. This highly diastereoselctive reaction has been applied to the asymmetric synthesis of polysubstituted tetrahydrofurans and γ‐lactones such as (+)‐eldanolide starting from achiral allylic alcohols and chiral vinyl ethers as depicted.