Visible Light-Induced Aerobic Oxygenation Reaction And Its Related Transformations

Molecular dioxygen has been widely utilized as an ideal terminal oxidant in organic synthesis because of its abundant,green,inexpensive,and environmentally friendly characters.However,it was found that the ground state oxygen,which exists in a triplet state(3O2)form,was difficult to be used as a direct oxidant of organic substrates due to its weak reactivity.Therefore,dioxygen activation for the functionalization of organic compounds has been of long-standing interest to organic chemists.As a novel and green strategy,visible light photocatalysis has been well applied to activate dioxygen for realizing the aerobic oxygenation reactions in the past several years.In this dissertation,we described the recent advances in this research area and the related visible light-induced aerobic oxygenation reactions were investigated.First,we developed an efficient sequential aerobic oxidation/semipinacol rearrangement reaction of 2,3-disubstituted indoles through visible light-induced photoredox catalytic generation of superoxide radical anion from dioxygen.This reaction could afford a wide range of synthetically significant 2,2-disubstituted indol-3-ones in generally good yields under mild reaction conditions.Moreover,we have studied the mechanism for this reaction via 180 labeling experiments,luminescence quenching experiments,and the detection of reaction intermediates.And the catalytic asymmetric variant of this transformation has also accomplished by merging visible light photocatalysis and chiral phosphoric acid catalysis.Moreover,based on the concept of "rational combination of two privileged backbones" for chiral ligand development,we designed and synthesized a novel visible light-responsive chiral ligand by grafting a triplet state photosensitizer(thioxanthone)to chiral bisoxazoline ligands.And the application of this ligand accomplished a visible light-induced photocatalytic asymmetric aerobic oxidation reaction of ?-ketoesters,affording the a-hydroxyl ?-ketoester products in high yields and enantioselectivities.More importantly,simply synthetic transformations of the hydroxylation products could give anti-1,2-diol and 1,2-amino alcohol with excellent stereoselectivities,which are useful synthetic blocks in asymmetric synthesis.And a plausible reaction mechanism and asymmetric induction model were proposed based on the mechanism studies.In addition,we have reported an aerobic oxidative C-B bond cleavage and ipso-hydroxylation of arylboronic acids mediated by methylhydrazine under metal-free conditions,using air as oxidant.This mild and metal-free transformation could afford structurally diverse phenols in good to excellent yields and showed a wide substrate scope and high functional group tolerance with respect to arylboronic acids.Moreover,the reaction could be carried out on a gram scale under the optimal conditions without any loss of efficiency.Finally,we have developed an intermolecular radical-radical cross-coupling reaction of amines with aryl ketones and aldehydes under visible light-induced photoredox catalysis.This reaction provides an efficient,environmentally friendly,and atom economic approach to the useful 1,2-amino alcohols from readily available amines and carbonyl compounds under mild condition.To demonstrate the synthetic utility of this method,the reaction has been performed on a gram scale or under direct irradiation of sunlight,delivering the desired product without loss of the reaction efficiency.