Acylsilanes with terminal alpha-stannyl bromide or xanthate functionalities are prepared. Alpha-stannyl radicals generated from these acylsilanes undergo intramolecular cyclizations to give cyclic silyl enol ethers regiospecifically. The radical processes involve radical cyclization, Brook rearrangement, and beta-fragmentation in sequence. A tributylstannyl group serves as the radical leaving group. The newly formed sigma-bond and pi-bond are located between the same two carbon atoms. This approach is limited to the formation of five-membered rings. In another route, omega-bromo-alpha-phenylsulfonylacylsilanes are synthesized. The radical cyclizations of these alpha-sulfonylacylsilanes also give cyclic silyl enol ethers. The phenylsulfonyl moiety is the radical leaving group in this system. Furthermore, the newly formed sigma-bond and pi-bond are located at adjacent positions sharing a single carbon atom. The latter approach is effective for both five- and six-membered ring formation.

The Application of Intramolecular Radical Cyclizations of Acylsilanes in the Regiospecific Formation of Cyclic Silyl Enol Ethers.-Two methods for the regiospecific formation of cyclic silylenol ethers are described. The first starts from α-stannyl bromide or α-stannyl xanthate derivatives and only leads to five-membered rings. The newly formed σ-bond and π-bond are located between the same C-atoms. The second one starts from ω-bromo-α-phenylsulfonylacylsilanes and allows effective preparation of five-and six-membered rings. In this case, the newly formed σ-bond and π-bond are located at adjacent C