Photocatalytic Asymmetric Michael Addition And C-H Bond Functionalization Of Tertiary Amines

The application of environmentally friendly light energy has become extremely important since the environment pollution is more and more serious.As a green and clean energy,light has long been used to mediate chemical reaction in photochemistry.Recently,photochemistry has been widely applied to organic synthesis and become the current popular research fields.In this paper,we introduced the latest research progress in the photocatalysis.Based on this strategy,we successfully realized asymmetric Michael addition and achieved the rapid synthesis of indole derivatives.Firstly,we presented the first example of asymmetric Michael addition of photogenerated o-quinodimethanes to ?,?-unsaturated ketones employing simple chiral amino acid esters as the catalyst.This reaction can be successfully applied to 3-substituted-2-cyclohexenones,and provides an efficient protocol for constructing the quaternary carbon centers with excellent stereoselectivities(up to 99%ee).The stereoselectivity was explained by DFT calculations for transition states of the C-C bond formation between the iminium intermediate and o-quinodimethanes.Secondly,we disclosed the direct functionalization of a sp3 C-H bond adjacent to the N atom of amines.But most of these transformations proceeded via the in situ generation of iminium intermediates,which are further attacked by a wide range of nucleophiles.Herein,we developed a new and broadly applicable alkylation of tetrahydroisoquinolines derivatives by radical-radical coupling with alkyl bromide reagents under photoredox catalysis.A variety of different bromide reagents were well tolerated,providing products in good yields(up to 89%yield).Meanwhile,we further applied the functionalization of a sp3 C-H bond adjacent to a tertiary nitrogen atom.This strategy was recognized as an ideal approach to synthesize indole derivatives through intramolecular dehydrated coupling reaction of tertiary amines and ketones(enones).Using Br(?)nsted acid as a cocatalyst,this method afforded indole derivatives in good to excellent yields(up to 92%)under visible light irradiation.