Study On CN-K-Based Heterogeneous Photocatalytic Alkylarylation Of Alkenes

Nitrogenous heterocyclic compounds,such as indolines,oxindoles,isoquinolinones and isoquinolinediones,are pivotal structural motifs in numerous pharmaceuticals,agrochemicals,and bioactive natural products.Alkylarylation of alkenes involving the key C-H functionalization of readily available acetonitrile is one of the most straightforward and powerful methods to access these useful structures.In recent years,although numerous protocols have been disclosed for the direct alkylarylation of alkenes,most of them rely on the use of transition metals,which always led to harsh reaction conditions and a limited range of substrate applications as well as considerable amounts of pollutant and waste.Recently,visible light-mediated photoredox catalysis has emerged as a powerful method in organic synthesis.In this context,Ir(III)and Ru(III)-based homogeneous photocatalytic systems has also been developed for this transformation.However,expensive and non-recyclable photocatalyst were required.Therefore,from the perspective of industrial practical applications,there is still an urgent demand to develop chemically stable,recyclable and low-cost heterogeneous photocatalysts to realize this useful transformation,enabling efficient and sustainable construction of valuable heterocyclic compounds under mild reaction conditions.In our previous study,we demonstrated potassium-modified carbon nitride(CN-K)exhibited remarkable activity for heterogeneous photocatalytic decarboxylative alkyl or acyl radical 1,6-addition and reductive dimerization of para-quinone methides.Inspired by this work,this thesis proposes CN-K could be served as an effective photocatalyst to generate alkyl radical from acetonitrile,which can then undergo radical addition/cyclization with a suitable nitrogen-containing alkene acceptor,furnishing the desired valuable nitrogenous heterocyclic compound.First,we chose alkylarylation reaction of N-aryl allylamine with readily available acetonitrile to construct indoline product as the model reaction.After systematic evaluation of reaction parameters including various radical initiators,different modified carbon nitride photocatalysts,light sources,reaction temperature and concentration,we obtained the optimal reaction conditions as follows:1 mg/m L of CN-K as the photocatalyst,CH₃CN as solvent,primary alkyl-substituted N-hydroxyphthalimide ester as radical initiator,24 W blue LED as light source and irradiation at 40 ^oC for 72 h.Then,the substrate scope was investigated.Variety of substrates including N-aryl allylamines,N-benzoyl allylamines,N-aryl acrylamides and N-benzoyl acrylamides could undergo this CN-K-based heterogeneous photocatalytic alkylarylation reaction smoothly,furnishing the corresponding nitrogenous heterocyclic products in high efficiency.To emphasize the practicability of this heterogeneous catalytic system,a recycling procedure was also successful established and the CN-K catalyst can be recycled at least five times without the loss of photocatalytic activity.The value of product was further demonstrated by a series of product derivatizations.Finally,based on the control experiments and previous work the reaction pathway was proposed.In summary,we have demonstrated in this thesis the application of a heterogeneous CN-K semiconducting photocatalyst in the alkylarylation of alkenes with acetonitrile utilizing readily available NHPI ester as radical initiator.This transition metal-free protocol tolerates a broad range of both unactivated and activated alkenes including N-aryl/benzoyl allylamines and acrylamides,providing a facile access to a series of structural diverse indolines,oxindoles,isoquinolinones and isoquinolinediones derivatives in high efficiency.The CN-K catalyst can be easily recovered from the reaction mixture and reused several times,illustrating the practicability and sustainability of this heterogeneous photocatalysis protocol.