Synthesis of branched-chain sugar derivatives related to aldgarose

Ethynylation of 1,2:5,6-di-O-isopropylidene-α-D-ribo-hexofuranos-3-ulose (1) gave the 3-C-ethynyl allo derivative 2, together with an adduct (3) resulting from interaction of two molecules of 1 with one of acetylene. Lithium aluminum hydride reduced the acetylenes 2 and 3 to the corresponding alkenes 4 and 8; on sequential ozonolysis-borohydride reduction, these both gave 3-C-(hydroxymethyl)-1,2:5,6-di- O-isopropylidene-α-D-allofuranose (6), further characterized as its 3,3¹-cyclic carbonate 9. Ozonolysis of the acetylene 2 gave the 3¹,5-lactone (5) of the 3-C-carboxy analog, thus establishing the stereochemistry of 2, which was independently established by n.m.r. spectroscopy employing a lanthanide shift-reagent. Treatment of 2 with mercuric acetate in ethyl acetate, followed by hydrogen sulfide, gave a mixture of the 3-C-acetyl-3-O-acetyl derivative 10 and a product (11) derived from internal cyclization of 5,6-deacetonated, O-deacetylated 10. Reduction of 10 with lithium aluminum hydride gave a separable mixture of diastereoisomeric 3-C-(l-hydroxy-ethyl) derivatives (12a, 12b) that were individually converted into their corresponding 3,3¹-cyclic carbonates 13a and 13b, products that contain the branch functionality of the unusual, branched-chain sugar aldgarose.