Study On Cycloaddition Reactions Of Alkynes For The Synthesis Of Cyclic Compounds

Organic cyclic compounds,including carbocycles,heterocycles,spirocycles,and bridged cyclic compounds,are the key structural motifs for many natural and biologically active compounds,as well as serve as particularly important synthetic intermediates.Accordingly,development of new synthetic methods for the preparation of cyclic compounds are of the important and ongoing area in synthesis.However,there are a few efficient synthetic approaches for the preparation of some important organic cyclic compounds,especially seven-membered cycles and more large cycles,with the common majority of examples requiring multi-step reactions,poor selectivity and limited substrate scope.Thus,new simple and effective methods for the synthesis of such componds would be of the most important aspects of synthetic organic chemistry and still remain challenging.Alkynes are one of most important intermediates in organic synthesis.Transformations of alkynes provide powerful tools to prepare a wide array of complex functionalized compounds.Among them,the cycloaddition of alkynes allows the formation of several new bonds in one operation and the synthesis of various ring skeletons with high atom-economy,excellent stereo-and regioselectivity.Further,the resulting C=C bond in products will provide a potential for further modifications.This dissertation mainly focuses on studying the Cycloaddition reactions of alkynes for the construction of application valuable organic ring compounds.The contents of this dissertation are summarized as follows:(1)Recent avances in the cycloaddition of alkynes are summarized detailedly.The cycloaddition reactions are classified and are discussed in this chapter.Three types of alkyne cycloadditon are described,including(i)the[5+2]cycloaddition reactions of alkynes,(ii)the[4+2]cycloaddition reactions of alkynes,and(iii)the other type cycloaddition reactions of alkynes.(2)In the second chapter,a novel FeCl3 and BF3·OEt2 co-catalyzed tandem hetero-[5+2]cycloaddition reaction of 2-(2-aminoethyl)oxiranes with a wide range of alkynes,including terminal alkynes and alkylsubstituted internal alkynes is presented.The reaction is the first example of rapid and facile production of diverse 2,3-dihydro-1H-azepines through a sequence of epoxide ring-opening,annulation,and dehydroxylation with broad substrate scope and exquisite selectivity control.Most importantly,employing an chiral substrate for the cycloaddition with alkynes,absolute configuration was remained during the cycloaddition process.Mechanistic studies showed that the reaction proceeded via a sequence of 2-(2-aminoethyl)oxirane ring opening,alkyne cycloaddition and E2 elimination.(3)A copper-catalyzed[4+2]cycloaddition of a-bromide phenylacetones with alkynes is described in the third chater.In the presence of Cu catalysts,cycloaddition cascade of alkynes is initiated by a carbon radical,which is genereated from a-bromide phenylacetones,thus allowing the formation three new C-C bonds and the synthesis of various ring-fused phenylnaphthalens with broad substrate scope and excellent selectivity control.The optimal reaction conditions include the use of 10 mol%Cu(MeCN)4PF6 as the catalyst,20 mol%phenanthroline as the ligand,2 equiv K2CO3 as the base,120?,toluene as the solvent,argon and 16 h.The control experiments showed a radical process.