Study On The Cyclization Reactions Of Aryl Azo Compounds

Aryl azo compounds has been widely used in pesticides and dye and photoelectric materials and organic synthesis,largely due to their nunique photochromic properties.Transition metal catalysis has been used in the synthesis of space-constrained azo compounds,enabling the activation and functionalization of C(sp~2)–H bond with excellent regio and chemoselectivity.The development of a green and efficient method for the functionalization of azobenzenes remains a big challenge.With the development of sustainable chemistry and utilization of clean energy,visible light catalysis has received increasing interests and become a hot topic in synthetic chemistry.In this thesis,the annulation of arylazo compounds by using both the transition metal catalysis assisted by C–H acticvation and visible light catalysis were explored and listed as follows:(1)With cesium fluoride as a base and acetonitrile as a reaction medium,the sunlight-promoted[3+2]cycloaddition of azobenzene with 2-(trimethylsiloxyl)phenyl trifluoromethesulfonate were examined,which enable the efficient construction of carbazole skeleton.The[3+2]cycloaddition of azobenzenes with arynes proceeded in absence of any transion metals or photosensitisers,generating the carbazole derivatives in moderate to good yields.Both the mechanistic studies and DFT calculation indicate the the sunlight irradiation led to the isomerization of azobenzene(E-Z),which is critical for the following[3+2]cycloaddition with arynes that in situ generated from(trimethylsilyl)phenyl triflates.(2)By using the strategy of directing group,a mild Rh(III)-catalyzed annulation of azobenzenes with vinylene carbonate in trifluoroethanol with silver(I)acetate as an additive has been established,which affords the a series of N-aryl-3-aldehyde(2H)–indazoles in moderate to good yields.This protocol features good group tolerance for symmetric and asymmetric azobenzenes.Particularly,the use of vinylene carbonate for the construction of indazole skeletone have never been reported.Based on the control experiments and mechanistic studies,a possible reaction mechsnim for the Rh(III)-catalyzed annulation of azobenzenes with vinylene carbonate was proposed.