Visible-light-induced Hydroacylation And Hydroalkylation Of Azobenzenes

Azobenzenes are not only important organic synthesis intermediates,but also play an important role in dyes,food,materials,pharmaceuticals,photopharmaceutical therapy,photomolecular switches,and other fields.Based on the increasing knowledge of the photoisomeric properties of azobenzene,the basic theories and reaction studies related to azobenzene and its derivatives have attracted great attention.In terms of organic synthesis reactions involving azobenzenes,compared to the traditional orthoC-H activation and further cyclization reactions,there are few reports on the addition reaction on the characteristic functional group N=N bond.In recent years,with the rapid development of contemporary organic photosynthetic chemistry,new opportunities have been provided to study the nature of the photoreactions of azobenzenes and to develop new reactions.In this regard,based on a thorough understanding of the mechanism and features of organic photosynthesis reactions and aimed at the lack of research on the addition reactions on the N=N bond of azobenzenes,the hydroacylation and hydroalkylation of azobenzenes were systematically investigated using visible-light reaction strategies and cheap and easily available raw materials in this thesis.The new methods for the corresponding reactions has been established and the reaction mechanism have clarified.(1)Using cheap and readily available aldehydes as acyl radical precursors,the hydroacylation of azobenzenes induced by visible light was systematically studied by photoredox and hydrogen transfer synergistic catalysis strategy.Upon the co-catalysis of photocatalyst Mes-Acr+ClO4-and hydrogen transfer catalyst thiophosphoric acid(TPA),the visible light-induced hydroacylation of azobenzene with aldehydes was successfully carried out at room temperature.The symmetrical and unsymmetrical azobenzenes as well as aromatic and aliphatic aldehydes with different functional groups reacted smoothly,and the target products N,N’-diaryl hydrazides were obtained in moderate to good yields.The established method has the advantages of abundant raw materials,mild conditions and wide substrate scope,which provides a novel and green way for the synthesis of N,N’-diaryl hydrazides.(2)Using thiols as alkyl radical precursor,the visible light-induced hydroalkylation of azobenzenes was achieved for the first time by merging photoredox catalysis and phosphoranyl radical chemistry,and a new method for the corresponding reaction was established.In the presence of a catalytic amount of Rose Bengal and stoichiometric triphenylphosphine,a series of azobenzenes reacted smoothly with thiols under visible light irradiation at room temperature.The hydroalkylation products of azobenzenes,N,N’-diaryl-N-alkyl trisubstituted hydrazines,were obtained in high yields.The mechanism studies show that alkyl radicals are produced by single electron oxidation of thiols and triphenylphosphine-mediated β-scission.This work has opened up a mild and efficient way for the synthesis of N,N’-diaryl-N-alkyl trisubstituted hydrazines.