Study On Denitrogenative And Cascade Transannulation Of 1,2,3-Triaza-aromatic Monocyclics

There are three nitrogen atoms continuously arranged on the parent rings of1,2,3-triaza-aromatic compounds,which compounds are generally convenient to construct and easy to transform.Among these transformation ways,denitrogenative transannulation is the most common one.Monocyclic 1,2,3-triazoles and 1,2,3-triazines are two representatives of these compounds.Based on the usual ways of denitrogenative transannulation,design practical reactions and strive to selectively construct structurally specific molecules in a concise way is our first guideline that this dissertation attempts to follow.Secondly,design cascade transannulation before and after denitrification for divergent synthesis,and strive to efficiently construct structurally diverse molecules with simple substrates.The third guideline is to screen proper substrates and conditions,design multi-component cascade reaction,and strive to realize compatible multi-step chemical transformation in a convenient operation.A coordinated combination of above three will certainly make the overall strategy attractive.However,coordinating and controlling the selectivity,reactivity and compatibility of the reaction will be an arduous challenge for subject,especially in a system with competitive reactions.The first chapter of this dissertation introduces the common construction methods and usual denitrogenative transannulation ways of 1,2,3-triazoles and 1,2,3-triazines,as well as the basic experimental conditions,in which each subject is carried out.The mainstay of dissertation is divided into five parts.In chapter 2,a new catalytic protocol to access synthetically challenging cis-2,3-dihydroazepines is reported.The reaction starts with readily available alkynes,sulfonyl azides and dienals,as the substrates and employs copper and rhodium as relay catalysts.Key steps include a copper-catalyzed reaction between an alkyne and a sulfonyl azide to form a triazole intermediate.The subsequent activation of this triazole intermediate by a rhodium catalyst,followed by a reaction with the dienal substrate,eventually leads to the dihydroazepine product.The regio-and stereochemistries of the products are believed to be controlled through a stereospecific conrotatory 8π-electrocyclization process against a possible competing 6π-electrocyclization process.In the following chapters 3 and 4,a multicomponent cascade reaction is described,which allows access to highly substituted benzenes and pyridines by combining four individual steps in a one-pot manner from the same set of readily available starting materials.The azepine intermediates were first used as the precursors for6π-electrocyclization to construct highly substituted benzenes and pyridines in a tunable manner.Chapter 5 of this dissertation demonstrates a concerted S_NAr reaction of1,2,3-triazines with phenols in which the nonclassic mechanism of this reaction could be revealed by calculation.Furthermore,the resulting 5-aryloxy-1,2,3-triazines could be used as convenient precursors to access biologically important 3-aryloxy-pyridines in one-pot manner.In chapter 6,a cascade addition reaction is disclosed,which started from1,2,3-triazines with thiols,and can obtained several differentα-substitutedβ-thio enals and their derivatives in a green,efficient and multi-step one-pot synthesis.At the end,the summary and prospect are presented.