In the past twenty years homogeneous gold(I) catalysis has been widely used as versatile tools for the generation of molecular complexity starting from simple substrates under mild conditions. In general, the intermolecular reaction of alkynes with alkenes catalyzed by gold are more challenging compare with the intramolecular ones due to competing side reactions and therefore less examples are reported. In this Doctoral Thesis we mainly focused on the development of a series of new gold(I)-catalyzed termolecular reactions of alkynes directly bounded to heteroatoms and we investigated their mechanism by means of experimental work and DFT calculations.
In the gold(I) catalyzed reactions of bromoalkynes with alkenes, the 1-bromo-cyclopropyl gold(I) carbene initially formed rearranges into gold(I) vinylidenes and vinylidenephenonium gold(I) cations passing through a cyclic bromonium intermediate. DFT calculations demonstrated that these two reactive intermediates are conformers of the same species but have different reactivity. On one side gold(I)-vinylidenes can undergo hydroarylation or C-H insertion, while vinylidenephenonium gold(I) cations easily undergo 1,2-aryl shift forming a triple bond.
Moreover, we found that terminal alkynyl ethers are undergoing efficiently [2+2] cycloaddition with alkenes to form cyclobutene derivatives that can be easily transformed into the corresponding cyclobutanones. In addition, internal alkynyl ethers react with a-methyl styrenes in a formal (4+2) cycloaddition to form chromanes.
To conclude we moved from homogenous gold(I) catalysis to focus on the development of the Ir(III)-catalyzed b-alkynylation of oximes derived from both alcohols and carbonyl compounds. The reaction displays an exquisite selectivity towards the primary C(sp3)-H bonds even when more activated aliphatic C-H bonds are present. The oxime directing group can be then removed under reductive conditions leading to b-alkynylated ketones or alcohols.
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