Synthesis of new C2-symmetric bioxazoles and application as chiral ligands in asymmetric hydrosilylation
作者:Sang-gi Lee、Chung Woo Lim、Choong Eui Song、In O Kim、Chul-Ho Jun
DOI:10.1016/s0957-4166(97)00353-4
日期:1997.9
chirality on their backbone, were synthesized efficiently starting from L-tartaric acid. The structure of 3a was determined by X-ray crystal structure analysis. With these novel chiral bioxazole ligands, as a preliminary investigation for their effects on the enantioselectivity, rhodium(I)-catalyzed enantioselective hydrosilylations of acetophenone were carried out.
Asymmetric cyclopropanation catalyzed by C2-symmetric bi(oxazolines)
作者:Rachel Boulch、Andreas Scheurer、Paul Mosset、Rolf W Saalfrank
DOI:10.1016/s0040-4039(99)02220-0
日期:2000.2
C-2-symmetric bi(oxazolines) 3a-e were prepared in three steps based on a tartaric-derived vicinal diamine as common precursor. These chiral ligands were studied with respect to their directive influence on the enantioselective copper catalyzed cyclopropanation of 1,1 -diphenylethylene and styrene. The highest enantioselectivities (79% ee) were achieved with bi(oxazoline) 3e, bearing bulky adamantyl groups even using commercial CuOTf. The presence of desiccants such as molecular sieves or magnesium sulfate was found to be crucial for high yields and reproducibility. (C) 2000 Elsevier Science Ltd. All rights reserved.