Chain Elongation of Aldoses by Indium-Mediated Coupling with 3-Bromopropenyl Esters

A procedure is described for acyloxyallylation of unprotected aldoses with two functionalized reagents:  3-bromopropenyl acetate and 3-bromopropenyl benzoate. The reaction is performed in ethanol or a dioxane/water mixture in the presence of indium metal. The products are deesterified in the workup to afford unsaturated polyols, which are isolated as mixtures of two diastereomers. The major diastereomers are subjected to ozonolysis to afford new aldoses, which have been elongated by two carbon atoms compared to the starting materials. The new aldoses all have lyxo configuration at positions 2, 3, and 4.