| Abstract
| - For the synthesis of 2‘,3‘-didehydro-3‘-deoxy-4‘-ethynylthymidine (8: 4‘-Ed4T), a recently reportedpromising anti-HIV agent, a new approach was developed. Since treatment of 1-(2,5-dideoxy-β-l-glycero-pent-4-enofuranosyl)thymine with Pb(OBz)4 allowed the introduction of the 4‘-benzoyloxy leaving group,nucleophilic substitution at the 4‘-position became feasible for the first time. Thus, reaction between the4‘-benzoyloxy derivative (14) and Me3SiC⋮CAl(Et)Cl as a nucleophile led to the isolation of the desired4‘-“down”-ethynyl derivative (18) stereoselectively in 62% yield. As an application of this approach,other 4‘-substituted nucleosides, such as the 4‘-allyl (24a) and 4‘-cyano (26a) derivatives, were synthesizedusing organosilicon reagents. In these instances, pretreatment of 14 with MeAlCl2 was necessary.
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