Stereoselective Formation of Eight-Membered Rings by Radical Cyclization of Silylenedioxy-Tethered Bis-methacrylate Derivatives

Radical-initiated addition of CCl4, Cl3CBr, PhSH, and (TMS)3SiH to (bisisopropyl)­silylene­dioxy-tethered bis-methacrylate derivatives gives the corresponding eight-membered ring cyclic adducts stereoselectively. Hydrolysis of halo-substituted cyclic adducts with HCl in methanol affords the corresponding valerolactones, and the stereochemistry was determined by the X-ray crystallography on a dibromobenzoate derivative. DFT calculation on the eight-membered radical intermediate offers a plausible rationale for the stereoselectivity of the reaction.