| Catalytic alkyne transformations,which are reported as efficient tools for the installation of various functional groups on the alkyne species,have the important impact in synthetic organic chemistry.In recent decades,transiton-metal catalyzed functionalization of alkynes has made a rapid progress due to its high efficiency on the formation of carbon-carbon and carbon-heteroatom bonds.And it not only has attracted considerable interests in organic chemistry,but also shown broad applications for the preparation of complex organic molecules in modern synthetic organic chemistry.Compared to the general catalytic alkyne transformations,the gold-catalytic approach has the advantages of chemoselectivity,regioselectivity,stereoselectivity,construction of compounds with structural diversity.In this thesis,readily available alkynes compounds and alkyne-tethered diazo compounds were applied as substrates to form heterocyclic compounds with potentially important biological activities via gold-catalyzed functionalization of alkynes.The first chapter is the summary of the advances on the gold-catalyzed functionalization reactions of alkynes published in recent years.In addition,the design of our research project and the main content of this thesis is also described.In the second chapter,a gold-catalyzed cyclization/carbonylation cascade reaction of 1,6-diynes is reported.The reaction goes through 6-exo-dig and 6-endo-dig cyclizations in sequence,and followed by hydration to provide the ?,?-unsaturated ketones with moderate to high yields under mild reaction conditions.In addition,according to the reported works on catalytic carbonylation of alkynes,this is the first example of intercepting the postulated 1,3-oxazine vinylgold intermediate with another pendant alkyne,which not only verifies the proposed mechanism,but also provides the ketone products with cyclized 1,2,3,6-tetrahydropyridine or 3,6-dihydro-2H-pyran frameworks from corresponding diynes.In the third chapter,a convergent formal[4+2]cycloaddition reaction for the construction of spiro-polycyclic frameworks has been disclosed.In this work,a tandem catalysis strategy is successfully established for the in situ generation of two reagents,a nonactivated cyclic alkyne and a reactive N-aryliminium ion,from the corresponding precursors 1,6-diyne and azide in the presence of gold(?)-catalyst and Br(?)nsted acid,respectively.Moreover,the current method presents the rare example of N-aryliminium ion[4+2]cycloaddition with trisubstituted alkenes,and synthesis structurally appealing spiro-tetrahydroquinolines with vicinal tertiary and quaternary carbon centers in high yieldsIn the chapter 4,we developed a novel gold-catalyzed water-mediated carbene cascade reaction of propargyl diazoacetates,which provides a general access for the synthesis of substituted furans in good yields with broad substrate generality under mild reaction conditions.Mechanistic investigation indicates that this reaction is initiated by the dinitrogen extrusion to form the gold-carbene,followed by an unprecedented 6-endo-dig carbocyclization with tethered alkyne through an oxonium ylide intermediate to generate the second gold-carbene species,which is terminated by a ?-H elimination/protodeauration process to give the aromatized furan products.In addition,the proposed gold-carbene intermediates are verified by interception experiments.In the chapter 5,we developed an efficient gold(?)-catalyzed carbocyclization reaction for the synthesis of isomycin derivatives from propargyl diazoacetates.The suggested cyclization pathway delineated the first example of a vinyl gold carbenoid species generated in situ from gold(?)-catalyzed 1,2-acyloxy migration of propargyl acetates containing a diazo functionality and the interception of the former by the latter through a cross-coupling reaction.Mechanistic studies also indicated that the use of appropriate protic additives was essential to regulating the reaction outcome by fine-tuning the catalytic preference of the gold(?)complex. |
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