Add time:08/30/2019         Source:sciencedirect.com

The addition of pyridin-2-yl-, (pyndin-2-ylmethyl)-lithium or lithium acetylide to 1,2:4,5-di-O-isopropylidene-β-d-erythro-2,3-hexodiulo-2,6-pyranose (1) affords the corresponding tertiary alcohol derivative in good yield with high stereo-selectivity. Some elimination of the 4,5-O-isopropylidene group of 1 occurs in the reaction with lithium acetylide, as well as with butyllithium, as shown by the formation of a 3-C-(2-oxopropyl) adduct and 5-deoxy-3-C-ethynyl-1,2-O-isopropylidene-β-d-glycero-2,4-hexodiulo-2,6-pyranose. Butyllithium and the Grignard reagents tested do not serve effectively as nucleophiles, but cause proton abstraction. and resultant decomposition. Chemical and n.m.r. -spectroscopic evidence shows that the addition products possess the β-d-ribo configuration and, probably, a slightly flattened 1C4(d) conformation. According to n.m.r. -spectral and rotatory data, 3-O-methyl derivatives of the branched alcohols exhibit a conformation more highly skewed, possibly 3S0, than that of the parent compounds. Among the compounds synthesized in establishing the configuration at the site of addition (C-3) were the 3,4- and 4,5-cyclic carbonates of 1,2-O-isopropylidene-3-C-(pyridin-2-yl)-β-d-psicopyranose.

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