Rhodium-Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to Nitroalkenes Using Olefin–Sulfoxide Ligands

An efficient rhodium/olefin–sulfoxide catalyzed asymmetric conjugate addition of organoboronic acids to a variety of nitroalkenes has been developed, where 2-methoxy-1-naphthyl sulfinyl functionalized olefin ligands have shown to be highly effective and are applicable to a broad scope of aryl, alkyl, and heteroaryl nitroalkenes

Ruthenium-Catalyzed [3 + 2] Cycloaddition of 2<i>H</i>‑Azirines with Alkynes: Access to Polysubstituted Pyrroles

A ruthenium-catalyzed intermolecular [3 + 2] cycloaddition of 2<i>H</i>-azirines and activated alkynes is reported, which provides polysubstituted pyrroles in moderate to good yields. This approach features a C–N bond cleavage of 2<i>H</i>-azirines by a ruthenium catalyst. The results of this study would provide a complementary method to synthesize polysubstituted pyrroles from the known 2<i>H</i>-azirine approaches and advance 2<i>H</i>-azirine chemistry

Regulation of the Co–N_<i>x</i> Active Sites of MOF-Templated Co@NC Catalysts via Au Doping for Boosting Oxidative Esterification of Alcohols

The Co–Nx active sites play a critical role over the Co@NC catalyst in the heterogeneous catalysis. However, the effective methods for the regulation of the content and electronic structure of Co–Nx active sites to enhance the catalytic efficiency of heterogeneous catalysts are still insufficient. Herein, a nitrogen-doped porous carbon-encapsulated Au-doped Co nanoparticle catalysts with abundant and electron-rich Co–Nx sites in the outer carbon layer was designed by a Au doping strategy through pyrolysis of the HAuCl4-modified ZIF-67 metal organic framework precursor. The optimal catalyst exhibits improved catalytic performance in alcohol selective oxidative esterification. The linear relationship between the ester yield and Co–Nx species content, combined with a series of control experiments, indicated that the Co–Nx active sites are crucial for achieving the excellent catalytic activity (yield: 99.9%). In situ diffuse reflectance infrared Fourier transform spectroscopy, O2-temperature-programed desorption characterizations, active oxygen species quenching experiments together with density functional theory calculations results indicate that Au doping in the Co nanoparticle core increases the content and the electron density of Co–Nx species on the outer carbon shell, which enhanced the chemical adsorption and activation of molecular O2 for producing reactive O2•– species. This study demonstrated a novel Co–Nx active site regulation strategy for the efficient selective oxidative esterification of alcohols under mild reaction conditions

Transition-Metal Controlled Diastereodivergent Radical Cyclization/Azidation Cascade of 1,7-Enynes

A strategy for achieving diastereodivergent azidations of enynes has been developed, employing azide transfer from the M–N₃ complex to alkyl radicals. Following this concept, the diastereoselectivity has been switched by modulating the transition metals and the ligands. The Mn­(III)-mediated radical cyclization/azidation cascade of 1,7-enynes afforded <i>trans</i>-fused pyrrolo­[3,4-<i>c</i>]­quinolinones, whereas the Cu­(II)/bipyridine system gave <i>cis</i>-products

Tf₂NH-Catalyzed Formal [3 + 2] Cycloaddition of Ynamides with Dioxazoles: A Metal-Free Approach to Polysubstituted 4‑Aminooxazoles

An unprecedented Tf₂NH-catalyzed formal [3 + 2] cycloaddition of ynamides with dioxazoles was developed to construct various polysubstituted 4-aminooxazoles. This approach features a metal-free catalytic bimolecular assembly of oxazole motifs, a low-cost catalyst, exceptionally mild reaction conditions, a very short reaction time, a broad substrate scope, and high efficiency. This metal-free protocol may find applications in pharmaceutical-oriented synthesis

Cyclization and <i>N</i>‑Iodosuccinimide-Induced Electrophilic Iodocyclization of 3‑Aza-1,5-enynes To Synthesize 1,2-Dihydropyridines and 3‑Iodo-1,2-dihydropyridines

Metal-free cyclization and <i>N</i>-iodosuccinimide-induced electrophilic iodocyclization of readily available 3-aza-1,5-enynes have been developed. The reactions selectively give 1,2-dihydropyridines and 3-iodo-1,2-dihydropyridines involving an aza-Claisen rearrangement and a 6π-electrocyclization step. Furthermore, the reaction could be carried out in 10 g scale for the synthesis of 1,2-dihydropyridines

Cyclization and <i>N</i>‑Iodosuccinimide-Induced Electrophilic Iodocyclization of 3‑Aza-1,5-enynes To Synthesize 1,2-Dihydropyridines and 3‑Iodo-1,2-dihydropyridines

Metal-free cyclization and <i>N</i>-iodosuccinimide-induced electrophilic iodocyclization of readily available 3-aza-1,5-enynes have been developed. The reactions selectively give 1,2-dihydropyridines and 3-iodo-1,2-dihydropyridines involving an aza-Claisen rearrangement and a 6π-electrocyclization step. Furthermore, the reaction could be carried out in 10 g scale for the synthesis of 1,2-dihydropyridines

In Situ Surface Engineering of Mesoporous Silica Generates Interfacial Activity and Catalytic Acceleration Effect

Mesoporous structured catalysts featuring interfacial activity are the most promising candidates for biphasic interface catalysis because their nanopores can concurrently accommodate catalytic active components and provide countless permeable channels for mass transfer between the interior and the exterior of Pickering droplets. However, to date, a convenient and effective strategy for the preparation of an anchor site-containing interfacial active mesoporous catalyst is still lacking. In the present work, we report a novel and efficient interfacial active mesoporous silica (MS) catalyst, which is prepared by a facile cocondensation of two types of organosilanes and subsequent anchoring of Pd NPs onto its surface through the confinement and coordination interactions. The as-prepared catalyst is then applied as emulsifier to stabilize the water-in-oil (W/O) Pickering emulsion and investigated as an interfacial catalyst for the hydrogenation of nitroarenes. An obviously enhanced rate toward the nitrobenzene hydrogenation is observed for the 0.8 mol% Pd/PAP-functionalized mesoporous silica-20 catalyst in the emulsion system (both conversion and selectivity are >99% within 30 min) in comparison to a single aqueous solution. Moreover, the emulsion catalytic system can be easily recycled six times without the separation of the catalyst from the water phase during the recycling process. This finding demonstrates that the incorporation of phenylaminopropyl trimethoxysilane amphiphilic groups during the hydrolysis of tetramethyl orthosilicate not only endows MS with interfacial activity but also improves the catalytic activity and stability

Cu-Catalyzed Ring Opening Reaction of 2<i>H</i>‑Azirines with Terminal Alkynes: An Easy Access to 3‑Alkynylated Pyrroles

A highly efficient Cu-catalyzed ring expansion reaction of 2<i>H</i>-azirines with terminal alkynes has been developed. This transformation provides a powerful method for the synthesis of 3-alkynyl polysubstituted pyrroles under mild conditions in good yields. The direct transformation process, specific selectivity, and good tolerance to a variety of substituents make it an alternative approach to the reported protocols

Synthesis of Polyfluoroalkyl Cyclobutenes from 3‑Aza-1,5-enynes via an Aza-Claisen Rearrangement/Cyclization Cascade

A facile synthetic route to access polyfluoroalkyl functionalized cyclobutenes bearing an exo cyclic double bond from 3-aza-1,5-enynes is reported. The reaction proceeds via a thermal aza-Claisen rearrangement to give an allene-imine intermediate; subsequent cyclization affords the cyclobutene core. The kinetics of the transformation of starting material and the intermediate was studied by ¹H NMR spectroscopy, where a consecutive reaction was revealed