Research On The Cyclization Reaction Of O-haloaniline,Isonitrile And Carbon Dioxide

Carbon dioxide is a greenhouse gas,and it can also serve as a nontoxic,abundant,cheap,easily available and renewable carbon resource.Carbon dioxide capture and utilization has attracted much attention of many scientists.Due to the thermodynamic stability and kinetic inertness of carbon dioxide,chemical utilization of carbon dioxide is difficult.However,carbon dioxide can be used as an important raw material for the synthesis of heterocyclic compounds with high added value through carboxylative cyclization reactions.This thesis developed a new palladium-catalyzed cyclization reaction system of o-haloaniline,isonitrile and carbon dioxide.Using Pd(CH3CN)2Cl2 as palladium source,SPhos as ligand,Cs2CO3 as base,DMSO as solvent,the electron-rich o-bromoaniline compounds reacted with tert-butylisonitrile and 2 MPa of carbon dioxide at 90 oC in 12 h to give the corresponding quinazolinedione products with high efficiency and high selectivity.Using Pd(OAc)2 as palladium source,PPh3 as ligand,CsF as base,the electron-deficient o-iodoaniline compound reacted with tert-butylisonitrile and carbon dioxide efficiently at room temperature.This reaction provides a convenient and feasible route to prepare the quinazolinedione compounds that are of great use in fine chemical synthesis.The possible mechanism of this reaction included the reaction of carbon dioxide with amino group to form the carbamate,the palladium(0)complex conducted oxidative addition reaction with aromatic halide to form a six-membered ring palladium complex,then isonitrile inserted into the carbon palladium bond to form a seven-membered ring palladium complex,followed reduction elimination reaction gave the benzoxazin-2-one-4-imine intermediate,which isomerized into quinazolinedione product under basic conditions.