Formal Synthesis of (+)-3-Deoxy-d- glycero-d-galacto-2-nonulosonic Acid (KDN) via Desymmetrization by Ring-Closing Metathesis

[figure: see text] Formal synthesis of the naturally occurring deaminated sialic acid KDN, a potential oncofetal antigen, has been accomplished in 45% overall yield via a novel ketalization/ring-closing metathesis sequence. The rapid introduction of all oxygen functionality in a completely stereocontrolled manner exploited a rigid 6,8-dioxabicyclo[3.2.1]oct-2-ene ring system. This general synthetic strategy should provide access to a number of KDN and sialic acid analogues.