Efficient Synthesis of 2′-Deoxy-β-D-furanosyl C-Glycosides. Palladium-Mediated Glycal-Aglycone Coupling and Stereocontrolled β- and α-Face Reductions of 3-Keto-furanosyl Moieties

Efficient routes for selective syntheses of 2′-deoxy-β-D-furanosyl C-glycosides have been developed and demonstrated by preparation of the isomers 5-[2′-deoxy-β-D-ribo- (=arabino)furanosyl]-1,3-dimethyl-2,4(1H,3H)-pyrimidinedione and 5-[2′-deoxy-β-D-xylo-(=lyxo)furanosyl]-1,3-dimethyl-2,4(1H,3H)-pyrimidinedione. The syntheses involved regio-and stereospecific palladium-mediated coupling of a new glycal, 1,4-anhydro-2-deoxy-3-O-[(1,1-dimethylethyl)diphenylsilyl]-D-erythro-pent-1-enitol with an appropriate aglycone derivative to form a single 2′-deoxy-3′-keto-β-D-furanosyl C-glycoside (as the corresponding silyl enol ether). Following desilylation, the ketone group of the furanosyl ring was reduced stereo-selectively in either of two ways: by delivery of hydride from (a) the most hindered face of the carbonyl carbon using sodium (triacetoxy)borohydride or (b) the least hindered face using potassium tri-(sec-butyl)borohydride.