Expedient conversion of D-glucose into 1,5-anhydro-D-fructose and into single stereogenic-center dihydropyranones, suitable six-carbon scaffolds for concise syntheses of the soft-coral constituents (-)-bissetone and (-)-palythazine

High-yielding protocols are described to convert D-glucose-via hydroxylaminolysis of its hydroxyglucal esters, followed by deoximination and beta-elimination of acid-into dihydropyranone building blocks with a single stereogenic center. Their versatility as enantiopure six-carbon scaffolds is highlighted by excellent regio- and stereocontrol in a variety of addition reactions and by their straightforward use as building blocks for the concise syntheses of the soft-coral constituents bissetone and palythazine in enantiopure form, thereby proving their absolute configuration. Moreover, several procedures are detailed to convert hydroxyglucal esters into 1,5-anhydro-D-fructose, their parent sugar, the direct low-temperature de-O-acylation being the most suitable for preparative purposes, as long as its access via enzymatic degradation of starch is not implemented on an appreciable scale. (C) 2008 Elsevier Ltd. All rights reserved.