Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.
Silver‐mediated reactions have recently emerged as a frontier area in organic chemistry. Indeed, the remarkable property of silver as a single‐electron oxidant has led to its exploitment into the field of radical chemistry. The excellent reactivity and high selectivity exhibited by silver salts in the activation of different organic substrates place them among the most prominent reagents in free radical reactions. The present review aims to provide the readers with a critical overview of silver‐based radical reactions, especially emphasizing the reactivity, selectivity and a detailed description of the reaction mechanism with particular attention to the role of Ag(I)‐based catalysts/reactants. The selected examples have been classified according to the type of radicals generated, namely carbon‐centered radicals and heteroatom (such as nitrogen, oxygen, phosphorus, sulfur)‐centered radicals. The generation of such radicals as well as their application in synthetic processes including oxidation, addition, coupling, and radical cascades have been described in detail.magnified image
A novel copper-mediated chelation-assisted ortho C-H nitration of (hetero)arenes has been developed for the first time, which used dioxygen as terminal oxidant and 1,2,3-TCP as solvent, leading to the synthesis of nitroaromatics with excellent regioselectivity and in good yields. Mechanistic investigations indicate a mechanism involving a four-centered transition state, with simultaneous cleavage of an ortho C-H bond and a N-O bond of the nitrate anion on the 2-arylpyridine-coordinated copper(II) complex.
An atom-economic route to thiophenes and bithiophenes has been developed starting from the readily available gem-dialkylthio enynes. A range of functionalized thiophenes and bithiophenes, bearing a pendent vinylthio group, were obtained in good to high yields under mild conditions.
An unexpected silver-catalyzed cascade reaction of β-enaminones and isocyanoacetates affording functionalized pyrrole derivatives is reported. In this reaction, tautomeric equilibria of β-enaminones are utilized to generate imine partners in situ. A hypothesized sequential Mannich addition/cyclization of imine tautomers and isocyanoacetates followed by an unprecedented ring-opening of the resultant 2-imidazolines and dehydration-condensation deliver the final 1,2,4,5-tetrasubstituted pyrrole products.
An efficient Ag CO -promoted sulfonylation of allyl/propargyl alcohols with sodium sulfinates has been developed. The reaction tolerates a wide range of functional groups to deliver γ-keto sulfones in high yields (up to 93 %). Propargyl alcohols furnished trimerization product 1,3,5-triaroylbenzenes in the presence of sodium methanesulfinate under the standard conditions. A mechanism involving a sulfonyl radical was suggested.
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