Pd-Catalyzed Synthesis Of Dibenzocarbazoles Via Tandem Annualtion Of Alkynylanilines

The synthesis and research of carbazole compounds has been an important subject in the fields of organic chemistry,medicinal chemistry and material chemistry.As a member of carbazole compounds,the benzocarbazole ring system is an important type of heterocyclic structure.The transition metal catalyzed C-H/C-N bond activation reaction to form a new C-C bond is an effective way for the cyclization reaction and also meets the development requirements of"green chemistry".This paper mainly introduces the reaction of Pd-catalyzed synthesis of dibenzocarbazoles via tandem annualtion of alkynylanilines,and during this reaction,it undergoes the C-H/C-N bond activation process.Finally,the possible mechanism will be discussed in this paper.Accompanied by the development of transition metal catalysis,a number of methodologies to construct the N-substituted dibenzocarbazole have been reported.The simplest method is the C-N coupling reaction,but this method requires the pre-synthesis of9-H dibenzocarbazole,this limits the application of this method.Other methods to synthesize N-substituted dibenzocarbazole,N-substituted indole is mainly used as a substrate,and the target structure is constructed by intermolecular or intramolecular reactions.Although various methods for synthesizing N-substituted dibenzocarbazole compounds have been developed,all of these methods require the formation of N-containing parent core structures in advance,such as carbazole or indole.How to optimize the reaction steps is a difficult problem in the synthesis of this important class of compounds.The tandem annualtion reaction is an effective method to build multiple chemical bonds in one step,but the synthesis of N-substituted dibenzocarbazoles compounds by this method has not been reported.In this paper,a series of o-alkynylaniline substrates were designed and synthesized.Then Alkynylaniline 3a was selected as a model substrate of this reaction,while the kind of catalyst,additive,oxidant and reaction solvent were investigated.The optimized reaction conditions are explored:PdCl₂（10 mol%）,MnO₂（3 equiv）,PivOH（1 equiv）,DMAc（0.2 M）,80℃for 12hours.On the basis of finding the optimal reaction conditions,we have introduced various substituents at different positions of the o-alkynylaniline substrate,systematically examined the effects of N-substitution effects of this Pd（I?）-catalyzed tandem annualtion reaction,After the experiment found:This reaction displayed broad substrate scope,good functional group tolerance,and high synthetic efficiency.A variety of alkynylanilines bearing different substituents can be directly converted into various functionalized dibenzo[a,c]carbazoles in good yields.Finally,we studied the reaction mechanism.Primary mechanistic study revealed that C-H bond activation is the rate-determining step of the reaction and it will undergo intramolecular nucleophilic addition reaction,nucleophilic substitution reaction of S_N2,C-H bond activation reaction,reduction reaction and oxidation reaction.All of products were characterized by ¹H-NMR,¹³C-NMR,HRMS.