Indium-mediated chain-extension: An improved protocol for the concise, diastereospecific synthesis of KDN and other sialic acids

Aqueous indium-mediated allylation of D-mannose with ethyl 2-(bromomethyl)a crylate leads, under acidic conditions, exclusively to the threo products i n high yields. A new purification procedure for indium-mediated reactions h as been developed which is based on a simple precipitation of indium-contai ning phosphate salts. This simplified protocol leads directly to diastereom erically pure KDN and other sialic acids, thus obviating the need for the u sual lengthy purification procedures.