A convenient access to the 1,5-anhydro forms of d-tagatose,l-rhamnulose and d-xylulose via 2-hydroxyglycal esters

Zemplén methanolysis or a three-step protocol comprising hydroxylaminolysis, de-O-acetylation and deoximination smoothly and efficiently convert the benzoylated 2-hydroxy-d-glycals of d-galactose, l-rhamnose and d-xylose into their configurationally related 1,5-anhydro-ketoses, thereby providing convenient access to the 1,5-anhydro forms of d-tagatose, l-rhamnulose and d-xylulose. Invariably obtained as amorphous solids, they are best characterized through their highly crystalline oximes.