Enantiomerically pure α-amino aldehydes from silylated α-amino acids

The disilylation of alpha-amino acids 1 to provide 2 (72-87%) was achieved without racemization. An unprecedented borane-mediated semi-reduction strategy was devised to convert 2 to stable, isolable oxazaborolidines 3 (100%) which were hydrolyzed to provide 5 (49-60%) as pure, stable compounds. Analysis of the Mosher amides (8) of the gamma-amino esters 7 reveals that <= 2% racemization occurs in the 1 -> 8 conversions.