C-C bond formation with acetylated 1-chloroglycopyranos-1-yl radicals, 2 stereocontrolled access to higher sugars (non-1-en-4-ulopyranosyl derivatives) and glycomimetics [3-(beta-D-glycopyranosyl)-1-propenes and (3Z)-4,8-anhydro-nona-1,3-dienitols]

Peracetylated 1-bromo-beta-D-glycopyranosyl chlorides react with allyltribu tyltin under photolytic conditions to afford the corresponding acetylated a lpha-D-non-1 -en-4-ulopyranosyl chlorides. Yields vary, depending mainly on the parent sugar configuration (D-gluco: 86%; D-galacto: 51%; D-manno: 31% ). The corresponding acetylated alpha-D-non-1-en-4-ulopyranoses resulting f rom hydrolysis were obtained as by-products (8-23% yield). Radical reductio n of the acetylated alpha-D-non-1 -en-4-ulopyranosyl chlorides, mediated by nBusSnH, led to glycopyranos-1-yl radicals, the diastereoselective quenchi ng of which produced acetylated 3-(beta-D-glycopyranosyl)- 1-propenes in go od overall yield (50-57 % yield). This approach, which combines C-C and C-H bond forming reactions involving glycopyranosyl radicals, constitutes a mo re efficient route to acetylated 3-(beta-D-glycopyranosyl)- 1-propenes. No traces of the 3-(alpha-D-glycopyranosyl) -1-propene epimers could be detect ed, so the diastereoselectivity of the radical-mediated reduction controlli ng the product structure was ascertained to be >95:5. On treatment with 1,8 -diazabicyclo[5.4.0]undec-7-ene (DBU), the acetylated 4-ulopyranosyl chlori des underwent stereoselective dehydrochlorination to afford new (3Z)-4,8-an hydronona-1,3-dienitols (42-63% yield), which could be deacetylated. Since these syntheses can be carried out by one-pot procedures, this work opens u p easy access to unsaturated C-glycopyranosyl compounds which are otherwise difficult to prepare or are completely unknown.