52] - Unsaturated Sugars via Cyclic Thionocarbonates, Cyclic Orthoformates, and Disulfonic Ester Intermediates: 5,6-Dideoxy-1,2-0-isopropylidene-α-D-xylo-hex-5-enofuranose, 3-0-Benzyl-5,6-dideoxy-1,2-0-isopropylidene-α-D-xylo-hex-5-enofuranose, and Methyl 4,6-0-Benzylidene-2,3-dideoxy-α-D-erythro-hex-2-enopyranoside

Abstract

This chapter focuses on unsaturated sugars through cyclic thionocarbonates, cyclic orthoformates, and disulfonic ester intermediates. Alkene-type unsaturation can be generated from terminal diol groups by forming a cyclic thionocarbonate and treating the latter with trimethyl phosphite. The procedure is effective with sugar derivatives even when an additional, unsubstituted hydroxyl group is present. The acid-catalyzed decomposition of a cyclic orthoformate provides a simple yet powerful process for converting a terminal diol group into an alkene, starting with a sugar derivative having all other hydroxyl groups protected. Vicinal diol groups in suitable carbohydrate derivatives can be converted by way of disulfonic ester intermediates into alkenes even when the hydroxyl groups are trans-disposed in a cyclic system.