Enantioselective Construction Of Carbon-heteroatom Bonds By Chiral Schiff Base

Chiral compounds are widely used in the fields of medicine, chemistry and biology, and thus the development of catalytic asymmetric synthesis of chiral moleculesvia chiral ligand-promted transformation is highly desired. In organo-metallic catalysis, chiral ligands play an important role because of its powerful potentials in the stereoselective induction in corresponding reactions. Among numerous liagnds, Schiff base have the strong ability to collaborate with most of metal center to form organometallic complexes, which proved the importance of such Schiffbases in the achieving the high level of catalytic performance in many reactions. In the field of asymmetric catalysis, chiral Schiff base is a very promising class of ligands, and it has been widely used in a variety of asymmetric synthesis. In this paper, based on a modular strategy, chiral Schiff base ligands with multiple stereogenic centers and multi-functional groups, has been successfully developed. And on the other hand, its application in asymmetric catalysis is also described.It was found firstly that the cinchonine and BINOL-derived multifunctional ligands bearing silicon-based bulky group exhibited promising enantioselective induction in the ruthenium-catalysed carbenoid N-H insertion reaction, in which the Ru-L26 system with multiple stereogenic centers was proved to be an enzyme-like catalyst because it exhibited narrow substrate scope and size-sensitive discrimination in this reaction.Then on the basis of present high-throughput screening of multifunctional Schiff base ligands that combined with aromatic aldehydes and chiral amino alcohols, the Schiff base bearing multifunctional N,O,O-groups with suitable electronic and steric effects was found to be effective Ti-linked ligands in the catalytic asymmetric bromochlorination reaction, in which the corresponding aromatic bromo-chloroalcohols with two bromide/chloride-linked carbon-stereogenic centers were obtained in moderate to excellentregio-and enantioselectivities (up to 93%ee) as well as good yields and chemoselectivities (up to 50:1 cr).