Development of New Silicon Tethers and Their Application to the Synthesis of Anti-HIV Nucleosides

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A novel radical method for the stereoselective introduction of an ethynyl group using ethynyldimethylsilyl (EDMS) or [2-(trimethylsilyl)ethynyl]dimethylsilyl (TEDMS) as the radical acceptor tethers has been developed. When a solution of EDMS or TEDMS ethers of trans-2-iodoindanoI was treated with Et_3B followed by tetrabutylammonium fluoride in toluene, atom transfer 5-exo-cyclization and subsequent elimination occurred to give cis-2-ethynylindanol in high yield. The method was shown to be useful in the introduction of an ethynyl group in various five and six-membered ring iodohydrins. Furthermore, 2'-deoxy-2'-C-ethynyluridine and cytidine, which were designed as novel anti-HIV nucleoside analogues, were readily synthesized using this method as the key step.