We have recently described' the reductive desulfonyloxylation of some secondary p-toluenesulfonates of glycosides by lithium triethylborohydride (Super Hydride@', LTBH), which afforded high yields of deoxy sugars. The glycosides used were 4,6-0-benzylidenated glycopyranoside 2-and 3-tosylates, and the reactions were demonstrated to proceed via 2,3_anhydroglycoside intermediates. In continuation' of these studies, a number of non-benzylidenated hexopyranoside tosylates, e.g., 1 and 2, were treated with LTBH in the same way, and, although desulfonyloxylation occurred with equal ease, it was accompanied by ring contraction, to give C-(hydroxymethyl)pentofuranosides (e.g., 3 from 2). For an assessment of the mechanism involved in this rearrangement of the glycose skeleton, it was necessary to decide whether or not there were formed intermediary epoxides in these instances, too, as in those of the benzylidenated series previously studied. Consequently, by independent routes, we prepared the known epoxides 4 and 7, and allowed them to react with LTBH under the conditions employed for the desulfonyloxylations mentioned. The epoxides underwent clean and facile reduction to the dideoxyhexopyranosides 5 and 8; isolated yields were >90%, and no products of ring contraction were detectable.
We now describe the preparative aspects of, and record some new data for, 5 and 8, which are glycosides of considerable interest.
Methyl 3,6-dideoxy-cY-D-xylo-hexopyranoside ( 5) is derived from abequose, a component of pyrogenic lipopolysaccharides isolated from Salmonella species3. Early syntheses4 of abequose departed from derivatives of 3-deoxy-D-xylo-hexose. Later on, Siewert and Westphal' synthesized the glycoside 5 by reduction of methyl 3,4-anhydro-6-O-p-tolylsulfonyl-c~-~-galactopyranoside (4) with lithium aluminum hydride in oxolane solution, which afforded a 61% yield. Similar reduction of the 6-deoxy analog of 4 gave 5 in 76% yield5, or almost quantitatively6. The syrupy