TMSCH2Li–LiDMAE: a new nonnucleophilic reagent for C-2 lithiation of halopyridines
作者:Abdelatif Doudouh、Philippe C. Gros、Yves Fort、Christopher Woltermann
DOI:10.1016/j.tet.2006.04.059
日期:2006.6
A new superbasic reagent has been discovered by combining TMSCHL(2)i and LiDMAE in hexane. This reagent was found highly efficient for the C-2 lithiation of sensitive chloro- and fluoropyridines. The metallation occurred chemo- and regioselectively at 0 degrees C avoiding the nucleophilic addition or substrate degradation commonly obtained with other alkyllithiums even at lower temperatures. (c) 2006 Elsevier Ltd. All rights reserved.
Biocatalytic preparation of optically active 4-(N,N-dimethylamino)pyridines for application in chemical asymmetric catalysis
4-Chloro-2-(1-hydroxybenzyl)pyridine and 4-chloro-2-(1-hydroxyalkyl)pyridines were obtained with moderate to excellent enantiomeric excesses and high isolated yields by bioreduction with Baker's yeast of the corresponding ketones. The resulting optically active alcohols were transformed into adequate DMAP derivatives, which have been applied in asymmetric catalytic processes as nucleophilic catalysts in the stereoselective chemical alkoxycarbonylation of 1-phenylethanol or as chiral ligands in the enantioselective addition of diethylzinc to benzaldehyde. (c) 2006 Elsevier Ltd. All rights reserved.