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  • Title: The application of intramolecular radical cyclizations of acylsilanes in the regiospecific formation of cyclic silyl enol ethers.
    Author: Huang CH, Chang SY, Wang NS, Tsai YM.
    Journal: J Org Chem; 2001 Dec 28; 66(26):8983-91. PubMed ID: 11749631.
    Abstract:
    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.
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