Silver-Catalyzed Cyclopropanation of Alkenes Using <i>N</i>‑Nosylhydrazones as Diazo Surrogates

An efficient silver-catalyzed [2 + 1] cyclopropanation of sterically hindered internal alkenes with diazo compounds in which room-temperature-decomposable <i>N</i>-nosylhydrazones are used as diazo surrogates is reported. The unexpected unique catalytic activity of silver was ascribed to its dual role as a Lewis acid activating alkene substrates and as a transition metal forming silver carbenoids. A wide range of internal alkenes, including challenging diarylethenes, were suitable for this protocol, thereby affording a variety of cyclopropanes with high efficiency in a stereoselective manner under mild conditions

Modular Synthesis of Sulfonyl Benzoheteroles by Silver-Catalyzed Heteroaromatization of Propargylic Alcohols with <i>p</i>‑Toluene­sulfonyl­methyl Isocyanide (TosMIC): Dual Roles of TosMIC

A new silver-catalyzed heteroaromatization of propargylic alcohols with <i>p</i>-toluene­sulfonyl­methyl isocyanide (TosMIC) has been developed that provides an efficient and modular approach to sulfonyl benzoheteroles. For the first time, TosMIC plays a dual role in one reaction: sulfonyl source and ligand. An unprecedented deoxysulfonylation/hydration/condensation reaction pathway is disclosed

Tandem O–H Insertion/[1,3]-Alkyl Shift of Rhodium Azavinyl Carbenoids with Benzylic Alcohols: A Route To Convert C–OH Bonds into C–C Bonds

Alcohols are among the most abundant and commonly used organic feedstock in industrial processes and academic research. The first tandem O–H insertion/[1,3]-alkyl shift reaction reported is between benzylic alcohols and rhodium azavinyl carbenoids derived from <i>N</i>-sulfonyl-1,2,3-triazoles, which provides a strategically novel way of cleaving C–OH bonds and forming C–C bonds. The substrate scope is broad, capable of covering 1°-, 2°-, and 3°-benzylic alcohols. Moreover, it constitutes a new and powerful synthetic method for constructing α-aminoketones. Mechanistic studies suggest that a [1,3]-alkyl shift of oxonium ylides is responsible for cleavage of the C–OH bonds

Radical Enamination of Vinyl Azides: Direct Synthesis of <i>N</i>‑Unprotected Enamines

An electron-withdrawing-group-generable radical-induced enamination of vinyl azides is reported, which results in a variety of β-functionalized <i>N</i>-unprotected enamines in a stereoselective manner. A plausible mechanism involving an unusual 1,3-H transfer of in situ generated iminyl radical intermediate was proposed on the basis of experimental results and DFT calculations

Silver-Mediated Direct C–H Cyanation of Terminal Alkynes with <i>N</i>‑Isocyanoiminotriphenylphosphorane

A direct cyanation of terminal alkynes for the synthesis of propionitrile derivatives, with the aid of silver salt using water additive, has been achieved. The cyano source used is <i>N</i>-isocyanoiminotriphenylphosphorane, which is nontoxic, safe, and easy to handle. This protocol is characterized by its operational simplicity, high efficiency with excellent yields, broad substrate scope, and greater functional group tolerance

Formation of Benzo[<i>f</i>]‑1-indanone Frameworks by Regulable Intramolecular Annulations of <i>gem</i>-Dialkylthio Trienynes

An atom-economic route to benzo­[<i>f</i>]-1-indanone frameworks has been developed starting from the readily available <i>gem</i>-dialkylthio trienynes by intramolecular annulations. The chemoselectivity of the intramolecular cyclizations can be regulated by both the base and the type of gas atmosphere used in the reaction, thus allowing the divergent synthesis of the corresponding functionalized benzo­[<i>f</i>]-1-indanones in good to excellent yields

Silver-Catalyzed Cascade Reaction of β‑Enaminones and Isocyanoacetates To Construct Functionalized Pyrroles

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

Synthesis of 4‑Ynamides and Cyclization by the Vilsmeier Reagent to Dihydrofuran-2(3<i>H</i>)‑ones

The room-temperature nucleophilic addition of vinyl azides to propargylic alcohols under BF₃·Et₂O catalysis provides an efficient synthesis of 4-ynamides. The procedure is operationally convenient, shows broad substrate scope, and is viable for the synthesis of multifunctional 4-ynamides. Further, a Vilsmeier intramolecular cyclization of 4-ynamides into dihydrofuran-2­(3<i>H</i>)-ones has also been discovered, which represents the first report of alkynes being used as the nucleophiles in Vilsmeier-type reactions

Silver-Catalyzed Tandem Hydroazidation/Alkyne–Azide Cycloaddition of Diynes with TMS‑N₃: An Easy Access to 1,5-Fused 1,2,3-Triazole Frameworks

A general cascade hydroazidation and alkyne–azide 1,3-dipolar cycloaddition of diynes using silver catalysis is reported. A wide variety of diynes participated in the reaction with trimethylsilyl azide (TMS-N₃) in the presence of H₂O, affording the corresponding 1,5-fused-1,2,3-triazoles in good-to-excellent yields. This unprecedented protocol is operationally simple with a broad substrate scope, good functional group tolerance, and high reaction efficiency, thus providing easy access to various fused 1,2,3-triazoles

Radical Mechanism of Isocyanide-Alkyne Cycloaddition by Multicatalysis of Ag₂CO₃, Solvent, and Substrate

A combined DFT and experimental study was performed to reveal the mechanism of isocyanide-alkyne cycloaddition. Our results indicate that the mechanism of this valuable reaction is an unexpected multicatalyzed radical process. Ag₂CO₃ is the pivotal catalyst, serving as base for the deprotonation of isocyanide and oxidant to initiate the initial isocyanide radical formation. After the cycloaddition between isocyanide radical and silver-acetylide, substrate (isocyanide) and solvent (dioxane) replace the role of Ag₂CO₃. They act as a radical shuttle to regenerate isocyanide radical for the next catalytic cycle, simultaneously completing the protonation. Furthermore, the bulk solvent effect significantly increases the reactivity by decreasing the activation barriers through the whole reaction, serving as solvent as well as catalyst