NaIO4-mediated asymmetric bromohydroxylation of α,β-unsaturated carboxamides with high diastereoselectivity: a short route to (−)-cytoxazone and droxidopa

The NaIO4-mediated asymmetric bromohydroxylation of α,β-unsaturated carboxamides was achieved using lithium bromide as the bromine source under acidic conditions at rt to afford the corresponding chiral α-bromo-β-hydroxy carboxamides. Excellent yields (77-90%) and diastereoselectivities (up to 10:1) along with exclusive control over regio- as well as anti-selectivity are the main features with a good scope of substrates. The method has successfully been applied in the enantioselective syntheses of two biologically important molecules, viz (−)-cytoxazone and l-threo-DOPS (droxidopa).