Synthetic routes to higher-carbon sugars. Reaction of lactones with 2-lithio-,3-dithiane

The per(trimethylsilyl) ether of d-glucono-1,5-lactone reacted with 2-lithio-1,3-dithiane to give, after removal of protecting groups, a 62% yield of 1-C-(1,3-dithian-2-yl)-α-d-glucopyranose (3) as a single tautomer; this product is formally a derivative of a 7-carbon, 1,2-dicarbonyl sugar. The crystalline 2,3,4,6-tetraacetate (4 of 3 was readily obtained, again as a single tautomer, and forcing conditions of acetylation led to the acyclic, enol hexaacetate in admixture with the cyclic pentaacetate (6) of 3. Desulfurization of the tetraacetate 4 with Raney nickel gave 1-deoxy-d-gluco-heptulose as its α-pyranose 3,4,5,7-tetraacetate, whereas similar desulfurization of the pentaacetate 6 was accompanied by removal of the tertiary acetoxyl group, providing stereospecific access to the C-β-d-glucosyl compound 2,6-anhydro-1-deoxy-d-glycero-d-gulo-heptitol as its 3,4,5,7-tetraacetate. To explore the effects of chain substituents on the tautomeric behavior of the lactone-derived adducts, the simple lactones 5-pentanolide, 4-butanolide, and 4-pentanolide were made to react with 2-lithio-1,3-dithiane, and the tautomeric compositions of the products were examined before and after acetylation. This work establishes preparative access to 1,2-dicarbonyl sugars, higher ketoses, and C-glycosyl compounds from readily available lactone precursors.