Visible-Light-Induced Radical Polynitration Of Arylboronic Acids:Synthesis Of Polynitrophenols

Visible light photocatalysis is a reliable and powerful tool for the development of green,sustainable and effective synthesis of fine chemicals.In recent years,more and more organic synthesis reactions using photocatalysis have been achieved,and in some respects they have demonstrated unparalleled advantages over conventional organic synthesis,such as high efficiency,mild reaction conditions and sustainability,while reducing a lot of by-products from heating.These reaction characteristics greatly increase the efficiency of synthesis,the atomic economy of the reaction,and make organic synthesis more environmentally friendly.Unlike traditional free radical chemistry,the generation of free radicals in a light-induced manner can avoid the use of toxic,expensive free radical initiators,and can greatly expand the types of free radical precursors.In the past few years,the application of visible light catalysts has facilitated the production of free radicals and promoted its targeted application in organic synthesis.The success of this strategy relies on a series of pioneering work by Mac Millan,Yoon,and Stephenson and other research groups using ruthenium and rhodium transition metal complexes as photoredox catalysts.However,the use of transition metal complexes has high cost,potential toxicity and other unfavorable factors.Therefore,visible light catalytic reactions without external photosensitizers have unique advantages.Aromatic nitro compounds are one of the most important classes of organic compounds used in pharmacology,agrochemicals,pesticides,polymers,dyes,and medicines.Conventional nitration reactions rely on strongly oxidizing mixed acid(HNO3/H2SO4)for the direct electrophilic nitration of aromatics.These harsh reaction conditions represent a remarkable limitation in terms of tolerance towards oxidation or acid-sensitive functional groups.Even though a great number of photo-promoted organic reactions have been reported in the past years,the photo-induced C–H nitration of aromatics remains unknown so far.In this work,we propose that the visible light-promoted tandem hydroxylation and nitration of arylboronic acids is a novel and efficient way to synthesize polynitroaromatic compounds.