Alkyne [3+2] Cycloaddition And [2+2+1] Cycloaddition For The Construction Of Five-Membered Ring Compounds

Alkynes are a class of the important basic structural units that widely presented in natural products,pharmaceutical molecules,and functional materials.Moreover,alkynes are common feedstock chemicals due to their low cost and high reactivity.Thus,transformations of alkyens have attracted extensive attention from chemists.The cycloaddition reaction has emerged as one of the most powerful synthetic methods for constructing diverse cyclic compounds.Among them,the[3+2]cycloaddition and[2+2+1]cycloaddition reaction is an important pathway for the synthesis of five-membered cyclic compounds.Five-membered rings,especially heterocycles,are important structural moitfs that widely found in natural products and pharmaceutical molecules.The[3+2]cycloaddition reaction of alkynes has become one of the most important methods for building highly valuable five-membered heterocyclic compounds in organic synthesis.This thesis mainly investigates transition metal-catalyzed[3+2]cycloaddition and[2+2+1]cycloaddition reactions of alkynes,and visible-light induced[3+2]cyclization and[2+2+1]cycloaddition reactions of alkynes,which are described detailedly as follows:（1）Recent progress in the[3+2]cycloaddition and[2+2+1]cycloaddition reactions of alkynes catalyzed by transition metals or visible light is comprehensively summarized.The transition-metal-catalyzed[3+2]cycloaddition and[2+2+1]cycloaddition reactions of alkynes mainly cover the experimetnts and mechanisms using palladium,rhodium,ruthenium,cobalt,nickel,copper,gold,and silver as the catalysts,Moreovethe experimental results and reaction mechanisms of the visible light-induced catalytic[3+2]cyclization reactions are also described and discussed.（2）A nickel-catalyzed asymmetric reductive[3+2]annulation of o-haloaromaticβ-alkenyl ketones with alkynes through alkyne dicarbofunctionalization and alkene isomerization cascades is disclosed,enabling the formation of highly enantiomerically enriched 1-alkenyl 1H-inden-1-ols that possess an important stereogenic quaternary carbon and an active alkene unit.This reaction shows notable features of a broad substrate scope and excellent controlled stereo-,chemo-,and regio-selectivity and is useful for synthetic applications to the construction of diverse chiral tertiary alcohol system-containing sterically demanding structures and their derivatized chiral building blocks.（3）A new,metal-free electron donor–acceptor（EDA）complex photocatalysis strategy for alkylative[3+2]annulation of N-alkyl isoquinolin-2-ium salts with common alkynes in ethyl acetate/H₂O to assemble highly functionalized pyrrolo[2,1-a]isoquinolines is presented.Upon photoinducing reactivity using the catalytic isoquinoline-based EDA complex,this method enables incorporation of alkynes as two-carbon units to achieve alkylative[3+2]annulation of N-alkyl isoquinolin-2-ium salts,and is notable for its excellent site selectivity,tolerance of a wide range of functional groups,the use of aqueous media and avoidance of the need for expensive external photocatalysts and basic or acidic promotors.Mechanistic study indicates that the EDA complex is generated from association of a catalytic isoquinoline with N-alkyl isoquinolin-2-ium salts to photoinduce reactivity.（4）An electron donor-acceptor（EDA）complex photocatalyed three-component alkylative[2+2+1]annulation of common terminal alkynes with isoquinolines and 2-bromomalonates to access pyrrolo[2,1-a]isoquinolines is presented,wherein isoquinolines serve as the reaction components and electron donors of the EDA complexes.The method is highlighted by the avoidance of the requirement of external photocatalysts and acidic promotors,good functional group tolerance and exquisite selectivity.Mechanistic study indicates that the EDA complex consists of isoquinolines coordinated with 2-bromomalonates,and the formation of N-alkyl soquinolin-2-ium intermediates is involved.