Radical-Involving Synthesis Of Pyridines?Pyrazols And Diazoindenes

Radical reactions have been highlighted as one of research frontier,widely used for total synthesis,the construction of carbo-and heterocycles,and the synthesis of functional small molecules,which are ascribed to their special features including mild reaction conditions,high compatibility with substrates containing functional groups,and wide compatibility with solvents as well as ease of quaternary center formation.In this dissertation,a series of novel aza-heterocycles involving in more complex structures were synthesized based on oxidants-mediated radical reactions.In these radical strategies,the starting materials have been maximized to convert into the desired molecules,avoiding isolation of intermediates and featuring atom economy,high synthetic efficiency and environmental friendliness.The discussions and results are listed as following:This paper is divided into four parts.The first section introduces the background of radical reactions in the application of synthesis of aza-heterocycles,especially in the construction of pyridines,pyrazole and diazo compounds.Furthermore,the topic selection,significance and novelty as well as research methods in this dissertation were also presented.The second section involves the high-efficient construction of fully substituted pyridines mediated by TBHP/I₂.The reaction of 2-?1-arylethylidene?malononitrile with several reactive sites and N-methylaniline was conducted in acetonitrile in the presence of TBHP and I₂,which underwent four-component oxidative dehydrogenation to give access to unreported fully substituted pyridines with good to excellent yields.The third section describes the synthesis of sulfonylated pyrazole derivatives under oxidative conditions.Benzoylacetonitrile were subjected to reaction with sulfonyl hydrazide in acetonitrile at room temperatures using TBAI/TBHP as a catalytic oxidation system,efficiently affording a series of pyrazole derivatives in good to excellent yields through radical-triggered[3+2]cyclization under mild reaction conditions.In the fourth section,the synthesis of new diazoindenes was achieved via sulfonyl radical-triggered reactions.Using enynals and sulfonyl hydrazide as starting materials and anhydrous TBHP/TBAI as a catalytic oxidation system,the reaction in mixed solvent of anhydrous acetonitrile and DMSO provided diazoindenes via arylsulfony radical-triggered 5-exo-trig carbocyclization.Some controlling experiments indicated that the reaction is a possible radical mechanism.The resultant diazoindenes was further reacted with phenylboronic acid,affording unprecedented hydrazine-tethered bifluorenes.All the structures of the resulting products were fully determined by their IR,NMR,HRMS.Possible radical-involving mechanisms were also proposed.The above these studies provide new and effective methods for the synthesis of potentially bioactive aza-heterocyclic compounds.