Search

Over the past two decades, the development and application of ynamide chemistry have received more and more attention. Ynamides have proven to be versatile reagents for organic synthesis, and have been widely applied to the rapid assembly of a diverse range of structurally complex N-containing molecules, especially the valuable N-heterocycles. In comparison with the well-established transition metal-catalyzed reactions of ynamides, metal-free ynamide transformations have relatively seldom been exploited. Recently, Brønsted acid-mediated reactions of ynamides represent significant advances in ynamide chemistry. This review summarizes the latest trends and developments of Brønsted acid-mediated reactions of ynamides, including cycloaddition, cyclization, intramolecular alkoxylation-initiated rearrangement, oxygen atom transfer reactions and hydro-heteroatom addition reactions. [ABSTRACT FROM AUTHOR]

A silver-mediated cascade trifluoromethylthiolation and cyclization has been developed for the synthesis of 2-(trifluoromethylthio)-indenones. A variety of arylpropynones underwent this radical oxidative cyclization with AgSCF 3 to afford trifluoromethylthiolated indenones in moderate to excellent yields. [ABSTRACT FROM AUTHOR]

Conspectus: This Account describes the use of quantum-chemical calculations to elucidate mechanisms and develop catalysts to accomplish highly selective cyclization reactions. Chemistry is awash with cyclic molecules, and the creation of rings is central to organic synthesis. Cyclization reactions, the formation of rings by the reaction of two ends of a linear precursor, have been instrumental in the development of predictive models for chemical reactivity, from Baldwin's classification and rules for ring closure to the Woodward and Hoffmann rules based on the conservation of orbital symmetry and beyond. Ring formation provides a productive and fertile testing ground for the exploration of catalytic mechanisms and chemo-, regio-, diastereo-, and enantioselectivity using computational and experimental approaches. This Account is organized around case studies from our laboratory and illustrates the ways in which computations provide a deeper understanding of the mechanisms of catalysis in 5-endo cyclizations and how computational predictions can lead to the development of new catalysts for enhanced stereoselectivities in asymmetric cycloisomerizations. [ABSTRACT FROM AUTHOR]

A series of benzylic substituted P,N-ligands 1 and 2 have been synthesized. The Pd-complexes of these ligands show high catalytic activity and enantioselectivity in catalyzing the asymmetric Heck reaction. A dramatic switch in enantioselectivity is realized using ligands with and without substituents at the benzylic position of the ligand. Ligands 1 with H as the substituents offer products in (R)-configuration while ligands 2 with the methyl as substituents result in (S)-configuration products. In most cases high enantioselectivities are achieved. Density functional theory calculations on the reaction mechanism as well as X-ray analysis of 1a-PdCI2 and 2a-PdCl2 complexes provide a rational explanation for the above observations. [ABSTRACT FROM AUTHOR]

Ynamides are electron‐rich heteroatom‐substituted alkynes with C−C triple bond directly tethered to the amide group. Over the past decades, ynamides have proven to be versatile reagents for organic synthesis and have received extensive attention. Compared with the well‐established ionic reactions of ynamides, radical‐based ynamide reactions have been exploited relatively seldom. Herein, radical reactions of ynamides, classified by radical attack at the α‐position and β‐position of ynamides, are reviewed by highlighting the reaction selectivity, scope, mechanism, and applicability. The aim of this review is to provide a comprehensive summarization of these advances, casting light on the further development of ynamide chemistry. [ABSTRACT FROM AUTHOR]

One-carbon homologation reactions based on one-carbon insertion into the N−O bond of heterocycles have received tremendous interest over the past decades. However, these protocols have to rely on the use of hazardous and not easily accessible diazo compounds as precursors, and examples of the relevant asymmetric catalysis have not been reported. Here we show that a copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles involving one-carbon insertion into the heterocyclic N−O bond via non-diazo approach. This method enables practical and atom-economic synthesis of valuable pyrrole-substituted oxadiazines in generally moderate to good yields under mild reaction conditions. In addition, the possibility of such an asymmetric formal (5 + 1) annulation also emerges. One-carbon insertion into N–O bonds is widely exploited in organic synthesis, but synthetic protocols for this rely on hazardous diazo precursors that are difficult to access. Here, copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles is shown to facilitate one-carbon insertion into heterocyclic N–O bonds without the need for diazo precursors. [ABSTRACT FROM AUTHOR]