De novo synthesis of galacto-sugar δ-lactones via a catalytic osmium/palladium/osmium reaction sequence

A highly efficient route to various 1,5-galacto-sugar lactones from dienoates has been developed by using three catalytic reactions. These reactions include (i) an enantioselective osmium-catalyzed dihydroxylation, (ii) a regio- and diastereoselective palladium-catalyzed π-allyl alkylation with p-methoxyphenol for alcohol differentiation and protection, and (iii) a diastereoselective dihydroxylation that can be improved using matched enantioselective osmium-catalyzed dihydroxylation condition.