Studies On Transition-metal-catalyzed C-H Functionalization

1.Study of the reaction of azobenzenes with terminal alkynes catalyzed by rhodiumThe cinnoline derivatives are important compounds in pharmarcy and material area,but few literature have been reported on the synthesis of these compounds.Moreover,the preparation of indole[1,2-b]cinnolines has not been reported yet.We developed a method to obtain indole[1,2-b]cinnolines through oxidative coupling between azobenzenes and terminal alkynes at 140 °C under inert atmosphere by using rhodium acetate as catalyst,copper acetate as oxidant,cuprous iodide as additive.This method is very efficient to obtain indolo[1,2-b]cinnolines with good tolerance for different functional groups in excellent atom economy.2.Study on the mechanism of reaction between azobenzenes and terminal alkynes catalyzed by rhodiumWe firstly put forward a synthesis method of rhodium catalyzed direct oxidative C-H acylation of azobenzenes with terminal alkynes to generate indole[1,2-b]cinnolines.We captured the Rh(IⅢ)complex formed during the reaction process,which could be an important reaction intermediate,and the complex was characterized by X-Ray structural analysis and NMR spectra.Meanwhile,we exploited an efficient method to get this complex.In addition,the Rh(III)complex was proved to be the real catalyst.Cu(ⅡI)should be the oxidant of Rh(I)to Rh(III),and Cu(Ⅰ)played an important role to improve yields.The oxygen atom in the product was indicated from the trace amount of water in the solvent after by the addition of H218O and characterized by HRMS.Eventually we proposed a plausible mechanism of this reaction according to the literatures and our reaction study.3.Synthesis of 2-Methylbenzoxazoles Directly from N-phenylacetamides Catalyzed by Palladium AcetateThe benzoxazole ring is a unique functional group.It has been widely used in the fields of drug molecules and functional materials,and therefore has always been a hot topic of organic chemists.People have been exploring its environmentally friendly synthesis methods for a long time.A method to synthesize 2-methylbenzoxazoles directly from N-phenylacetamides catalyzed by Pd(OAc)2 in the presence of K2S2O8 and TfOH.The desired products were obtained in moderate to excellent yields.This approach provides a facile procedure to prepare benzoxazoles with available substrates.It is found that TfOH is the key factor for this cyclization reaction.The plausible mechanism of the reaction is proposed according to the control reactions and the literatures.