Pd/Co-catalyzed Isocyanide Coupling Reactions

Isocyanide is an important reactive reactant containing stable divalent carbon atoms,which has been widely used in the construction of nitrogen compounds,new drugs and natural products.Recently,isocyanides have found a new application as versatile C1 building blocks in transition metal catalysis.The transition metal catalyzed reactions involving isocyanide insertion offer a vast potential to construct C-C or C-N bonds for the synthesis of nitrogen-containing fine chemicals.This paper mainly focuses on the oxidative coupling reactions of isocyanides catalyzed by Pd and Co,as well as the involvement of the S₃^·-in electron-catalyzed sulfur insertion reactions.The work mainly consists of the following two parts:Part I,（1）A method for palladium-catalyzed cascade reactions of isocyanides with enaminones has been developed.This methodology provides a direct approach to 4-aminoquinoline derivatives under mild conditions.（2）An efficient and practical synthesis of benzothiazine by K₂S initiated sulfur insertion reaction with enaminones via electron catalysis is developed.This protocol provides a new,environment-friendly and simple strategy to construct benzothiazine derivatives via two C-S bonds formation under transition metal-free,additive-free and oxidant-free conditions.K₂S not only provide the sulfur insertion source,but also ignites the reaction through the formation of trisulfur radical anion and electrons in DMF.（3）A chemoselective palladium-catalyzed isocyanide insertion with enaminones for the synthesis of amide derivatives via C-H functionalization and hydrolysis,or4-aminoquinoline derivatives via C-H functionalization involving 1,3-palladium migration has been developed.（4）A palladium-catalyzed intramolecular Heck reaction and aminopalladation of N-（2-（1-phenylvinyl）phenyl）aniline for the efficient synthesis of dihydroindeno[1,2,3-kl]acridines and 3-arylindoles via tuning the phosphine ligands and solvents under two optimized conditions are reported.The reaction follows a 1,4-Pd migration,aminopalladation,C（sp²）-H activation,as well as five-and six-membered-ring fusion to form different products.The dihydroindeno[1,2,3-kl]acridine derivatives showed higher triplet energies（E_T）levels than common blue phosphorescent dopant,which may serve as good host candidates for blue triplet emitters.Part II,（1）A cobalt-catalyzed[4+1]cycloaddition of easily accessible amides with isocyanides for the efficient synthesis of 3-iminoisoindolinone derivatives in high yield under mild conditions via intramolecular C（sp²）-H activation and isocyanide insertion is reported.The annulation was found to be applicable to a broad range of substrates,including arylamides,heteroarylamides,and acrylamide derivatives.Strongly coordinating N-heterocyclic directing groups,such as pyridine,pyrimidine and even pyrazole,were fully tolerated in this cobalt-catalyzed C-H activation reactions.（2）A Co（II）-catalyzed synthesis of sulfonyl guanidines by using amines,isonitriles,and organic azides as nitrene source has been developed.This protocol provides an environmentally-friendly,and simple strategy for the synthesis of sulfonyl guanidine derivatives by employing a range of substrates and will find potential applications in organic synthesis.The computational and EPR studies suggested the formation of guanidine derivatives via a cobalt-nitrene radical intermediate.（3）A chemoselective Co（II）-catalyzed effective synthesis of sulfonylamidyl amide and 3-imine indole derivatives by using isocyanides and sulfonyl azides has been developed.This protocol provides a new,environment-friendly and simple strategy for the efficient synthesis of the sulfonylamidyl amide and 3-imine indole derivatives with a wide range of substrates in the absence of any oxidants and additives.（4）A Co（II）-catalyzed effective synthesis of amidinium imine derivatives with isonitriles and boric acids using organic azides as nitrene source has been developed.The reaction enables the construction of a C-N double bond and two C-C bonds under simple and mild conditions,as well as the coupling reaction of boric acid under cobalt catalysis.