Synthesis related to the octodiose in apramycin. Part III

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Abstract
A synthesis of methyl 2,3-di-O-benzyl-7,8-dideoxy-4-O-methylthiomethyl-D-glycero- and L-glycero-α-D-gluco-oct-7-enopyranoside (11 and 12) has been achieved by the reaction of methyl 2,3-di-O-benzyl-4-O-methylthiomethyl-α-D-gluco-hexodialdo-l,5-pyranoside (9) with vinylmagnesium bromide; the stereochemistry at C-6 was established by degradation of 12 to the enantiomer of a known heptose derivative. Olefin 12 was converted, in six steps, into a mixture of dialdose derivatives 18 and 19 from which methyl glycosides 21 and 20, respectively, were prepared and shown to have the desired trans-decalin structure. The stereochemistry at C-7 in glycosides 20 and 21 was established by nmr spectroscopy.An intramolecular reaction involving the methylthiomethyl function has been observed and shown to give rise to O-methylene derivatives.