Highly enantioselective cyanosilylation of ketones catalyzed by a bifunctional Ti(IV) complex
作者:Ke Shen、Xiaohua Liu、Qinghan Li、Xiaoming Feng
DOI:10.1016/j.tet.2007.10.093
日期:2008.1
A bifunctionalcatalyst system composed of (S)-prolinamide (2a), titanium(IV) isopropoxide, and phenolic N-oxide (3f) exhibited high catalytic efficiency in the enantioselectivecyanosilylation of ketones. In the presence of 2.5 mol % catalyst, a variety of aromatic and aliphatic ketones were converted into the corresponding tertiary cyanohydrin O-TMS ethers in excellent yields (up to 96%) and high
A novel C2-symmetric chiralN,N′-dioxide titanium complex was described, which could efficiently catalyze the asymmetric cyanosilylation of ketones in high yields with up to 92% ee under mild conditions. In addition, the catalyst system was simple and the ligands could be easily prepared from commercially available chiral amino acid.
An efficient and optically active, bifunctional tetraaza ligand (2S)-N-(1R,2R)-2-[(S)-pyrrolidine-2-carboxamido]-1,2-diphenylethyl}pyrrolidine-2-carboxamide has been developed for the addition of trimethylsilyl cyanide (TMSCN) to ketones. The bifunctionalcatalyst system based on a monometallic titanium complex was found to be a highly enantioselectivecatalyst to provide O-TMS cyanohydrins with up