Abstract
Reaction of propargylmagnesium bromide with 2,3;5,6-di-O-isopropylidene-D-mannonolactone followed by highly stereoselective reduction of the so-formed lactol with sodium borohydride gives a syn-diol from which practical syntheses of 2-keto-3-deoxy-D-glycero-D-galactononulosonic acid (KDN) and various partially protected derivatives have been achieved all of which feature the oxidative unmasking of the α-keto acid moiety from the alkyne.