Directly Linked C-Disaccharides: Structures of Two 3,4-Dihydro-2H-pyran Derivatives

Analysis of the crystal structures of the two diastereomeric C-disaccharides, (2R,4R)-4-(1,2;3,4-di-O-isopropylidene-α-D-galacto-1,5-pyranose-5-yl) −2-ethoxy-6-(2-thiazolyl)-3,4-dihydro-2H-pyran, C₂₁H₃₁NO₇S, (3), and (2R,4S)-4-(1,2;3,4-di-O-isopropylidene-α-D-galacto-1,5-pyranose-5-yl) −2-ethoxy-6-formyl-3,4-dihydro-2H-pyran, C₁₉H₂₈O₈, (4), allows the definition of the absolute configurations of the products of the cycloaddition reaction between 1-oxa-1,3-butadiene and ethyl vinyl ether. The relevant conformational aspects of the two mol­ecules are discussed. In the crystals of (3) a water molecule participates in hydrogen bonds to the thiazole N atom and an O atom of a dioxapentane ring of the sugar moiety within the same molecule.

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