Enantio- and chemoselective Bronsted-acid/Mg(nBu)2 catalysed reduction of α-keto esters with catecholborane

The first enantio- and chemoselective Bronsted-acid catalysed reduction of alpha-keto esters with catecholborane has been developed. The alpha-hydroxy esters were obtained under mild reaction conditions in virtually quantitative yields and excellent enantioselectivities. With slight modifications both enantiomers can be obtained without any loss of selectivity.