De Novo Enantioselective Syntheses of <i>Galacto</i>-Sugars and Deoxy Sugars via the Iterative Dihydroxylation of Dienoate

An efficient route to various sugar lactones has been developed. Key to the overall transformation is the sequential osmium-catalyzed dihydroxylation of 2,4-dienoates. The simplest (one-step/racemic) example of this reaction occurs when the dihydroxylation is performed with aqueous NMO in MeOH. When the first dihydroxylation is performed using the AD-mix procedure, an enantioselective variant results. When a matched AD-mix procedure is used for the second dihydroxylation, an exceedingly diastereo- and enantioselective synthesis of <i>galacto</i>-1,4-lactone results.