Kiliani reactions on ketoses: branched carbohydrate building blocks from D-tagatose and D-psicose

D-Tagatose and D-psicose on treatment with sodium cyanide gave mixtures of branched sugar lactones; extraction of the crude products by acetone in the presence of acid permits direct access to branched carbohydrate diacetonides, likely to be of value as new chirons. In both cases, the major lactone products-diacetonides with a 2,3-cis-diol relationship-can be crystallised in around 40-50% yield from the ketohexose. A practical procedure for the conversion of 30 g of D-tagatose to give 24 g of 2,3:5,6-di-O-isopropylidene-2-C-hydroxymethyl-D-talono-1,4-lactone is reported.