Building Higher Carbohydrates via Dioxanone Aldol Chemistry: The α,α′-Bisaldol Approach

A synthetic approach to higher carbohydrates via the sequence of two aldol reactions that proceed at the α and α′ positions of 2,2-dimethyl-1,3-dioxan-5-one (dioxanone) is described. As reported before, the first aldol reaction works well under organocatalytic conditions (proline catalysis), this is followed by protection of the hydroxy, deprotonation of the resulting compound using excess of LDA, and the second aldol addition. This sequence of reactions gives compounds having a straight-chain carbon skeleton with an oxygen-based functional group at each carbon. Most of the groups are protected. The utility of this strategy is illustrated by short syntheses of 6-C-phenyl-D-glycero-D-allo-hexopyranose and D-erythro-D-allooctopyranose(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)