Kinetic resolution of sterically hindered racemic alpha-tert-alkyl-alpha-hydroxy esters is performed by enantiomer-selective carbamoylation with the t-Bu-Box-Cu(II) catalyst (Box = bis(oxazoline)). The reaction with 0.5 equiv of n-C3H7NCO is carried out with a substrate-to-catalyst molar ratio of 500-5000 at -20 to 25 degrees C. The high enantiomer-discrimination ability of the catalyst achieves an excellent stereoselectivity factor (s = k(fast)/k(slow)) of 261 in the best case. A catalytic cycle for this reaction is proposed.
Enantio- and chemoselective Brønsted-acid/Mg(<sup>n</sup>Bu)<sub>2</sub> catalysed reduction of α-keto esters with catecholborane
作者:Dieter Enders、Bianca A. Stöckel、Andreas Rembiak
DOI:10.1039/c4cc00427b
日期:——
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.