Stereodivergent Synthesis of D,D- and L,L-glycero-beta-allo-Heptopyranoses on a Dioxanone Scaffold

We report a stereodivergent synthesis of both enantiomers of glycero-allo-heptose from 2,2-dimethyl-1,3-dioxan-5-one, a readily available nonchiral scaffold, and from two different synthetic equivalents of glyoxal: dimethoxyacetaldehyde and 1,3-dithiane-2-carboxaldehyde. The short synthetic sequence involves first a proline-mediated, and then a lithium enolate mediated aldol reaction at the alpha-and alpha'-positions of the dioxanone ring, respectively, and demonstrates the complementary nature of organocatalysis and metal enolate based methods.