Serine as chiral educt for the practical synthesis of enantiopure N-protected beta-hydroxyvaline

N-tert-Butyloxycarbonyl- and N-benzenesulfonyl-beta-hydroxyvalines 1a and 1b were, respectively, synthesized in enantiomerically pure form by a two-step protocol from their enantiomeric N-protected serine methyl esters 2a and 2b. The addition of CH(3)MgBr to 2a and 2b provided diols 3a and 3b, respectively as major products in 83% and 81% yields. Selective oxidation of diols 3a and 3b was performed using a TEMPO, NaClO(2), NaOCl cocktail in 96% and 93% respective yields. This two-step process effectively furnished multigram amounts of enantiopure N-Boc-beta-hydroxyvaline 1a.