Stereocontrolled Access to Higher Sugars (Non-1-en-4-ulopyranosyl Derivatives) and Glycomimetics [3-(β-D-Glycopyranosyl)-1-propenes and(3Z)-4,8-Anhydro-nona-1,3-dienitols]

Peracetylated 1-bromo-β-D-glycopyranosyl chlorides react with allyltributyltin under photolytic conditions to afford the corresponding acetylated α-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 α-D-non-1-en-4-ulopyranoses resulting from hydrolysis were obtained as by-products (8−23% yield). Radical reduction of the acetylated α-D-non-1-en-4-ulopyranosyl chlorides, mediated by nBu3SnH, led to glycopyranos-1-yl radicals, the diastereoselective quenching of which produced acetylated 3-(β-D-glycopyranosyl)-1-propenes in good overall yield (50−57% yield). This approach, which combines C−C and C−H bond forming reactions involving glycopyranosyl radicals, constitutes a more efficient route to acetylated 3-(β-D-glycopyranosyl)-1-propenes. No traces of the 3-(α-D-glycopyranosyl)-1-propene epimers could be detected, so the diastereoselectivity of the radical-mediated reduction controlling 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 chlorides underwent stereoselective dehydrochlorination to afford new (3Z)-4,8-anhydronona-1,3-dienitols (42−63% yield), which could be deacetylated. Since these syntheses can be carried out by one-pot procedures, this work opens up easy access to unsaturated C-glycopyranosyl compounds which are otherwise difficult to prepare or are completely unknown.