Synthesis and Conformational Analysis of New Cyclobutane-Fused Nucleosides^†

A stereselective synthesis of 3-oxabicyclo[3.2.0]heptane nucleoside analogues, which were designed as conformational mimics of the anti-HIV
agents 2‘,3‘-didehydro-2‘,3‘-dideoxythimidine (stavudine, d4T) and 2‘,3‘-didehydro-2‘,3‘-dideoxyadenosine (d4A), is described. The target
compounds were prepared by condensation of a common intermediate bicyclic acetate, derived from a homochiral 2(5H)-furanone, with pyrimidine
and purine bases under modified Vorbrüggen conditions. The conformational behavior of the synthesized nucleoside analogues was studied
by NMR spectroscopy and X-ray crystallography.