Visible-Light-Driven Ni-DBFOX Catalyzed Asymmetric Radical Conjugate Addition

Cooperative catalysis is a strategy which uses several different catalysts to cocatalyze one reaction or one single catalyst to bifunctionally activate the substrates.It provides an effective approach to construction of inert bonds or setting up multiple stereocenters.In particular,cooperative catalysis has broad applications in asymmetric catalysis.However,in the developed dual catalytic systems or bifunctional catalysts,there are typically several issues need to be further address,for example,compatibilities of the different catalysts or catalytic cycles,high catalyst loadingsand limited reaction scopes.Hence,it is still highlyimportant to develop new bifunctional catalytic systems for different organic transformations.In this thesis,we will disclose our discovery of the first nickel catalyzed asymmetric photoredox reaction,in which the chiral nickel catalyst is involved in not only intiation of the visible-light-promoted single electron transfer,but also control of the stereochemical during the radical transformations.In addition,we demonstrate our effert on developing novel bifunctional chiral catalysts concerning metal-ligand cooperative effects.In Chapter 1,the research background of dual catalysis and bifunctional catalysis based on transition metal chiral complexes is briefly introduced.In Chapter 2,we disclosed our discovery that the readily available NiII-DBFOX complex can effectively catalyze the asymmetric photoredox reaction betweenα-silylamines and α,β-unsaturated carbonyl compounds.As a bifimctional catalyst,the chiral nickel complex is not only involved in a photo-induced single electron transfer process to initiate formation of the radical species,but also activates theα,β-unsaturated carbonyl substrates as a Lewis acid and governs the radical transformation in an enantioselective fashion.Good to excellent yields and enantioselectivities were achieved for the chiral y-amino carboxylic acid derivatives and y-lactam products.In view of the non-precious,low-toxic metal salt,readily available chiral ligand,mild reaction conditions and high asymmetric induction,this strategy might provide new opportunities to develop cheap and green synthesis of chiral molecules..In Chapter 3,we introduce metal-ligand cooperative effects for the design of novel bifunctional chiral catalysts.Two classes of bifunctional complexes bearingβ-NH or(β-basic groups have been synthesized and characterized.In the primary study on the catalytic properties,we found that these complexes didn’t exhibit activity in asymmetric Michael addition.The further investigation is on going in the laboratory.In Chapter 4,summary and prospect of this thesis are briefly discussed.