Amidation‐Dominated Re‐Assembly Strategy for Single‐Atom Design/Nano‐Engineering: Constructing Ni/S/C Nanotubes with Fast and Stable K‐Storage

An amidation‐dominated re‐assembly strategy is developed to prepare uniform single atom Ni/S/C nanotubes. In this re‐assembly process, a single‐atom design and nano‐structured engineering are realized simultaneously. Both the NiO₅ single‐atom active centers and nanotube framework endow the Ni/S/C ternary composite with accelerated reaction kinetics for potassium‐ion storage. Theoretical calculations and electrochemical studies prove that the atomically dispersed Ni could enhance the convention kinetics and decrease the decomposition energy barrier of the chemically‐absorbed small‐molecule sulfur in Ni/S/C nanotubes, thus lowering the electrode reaction overpotential and resistance remarkably. The mechanically stable nanotube framework could well accommodate the volume variation during potassiation/depotassiation process. As a result, a high K‐storage capacity of 608 mAh g^?1 at 100 mA g^?1 and stable cycling capacity of 330.6 mAh g^?1 at 1000 mA g^?1 after 500 cycles are achieved.     

Rhodium/Silver‐Cocatalyzed Transannulation of N‐Sulfonyl‐1,2,3‐triazoles with Vinyl Azides: Divergent Synthesis of Pyrroles and 2 H‐Pyrazines

The first cyclization reaction between vinyl azides and N‐sulfonyl‐1,2,3‐triazoles is reported. A Rh/Ag binary metal catalyst system proved to be necessary for the successful cyclization. By varying the structure of vinyl azides, such reaction allows the divergent synthesis of pyrroles and 2H‐pyrazines. The cyclization reactions feature a broad substrate scope, good functional group tolerance, high reaction efficiency, and good to high product yields.     

Palladium‐Catalyzed/Norbornene‐Mediated CH Activation/ N‐Tosylhydrazone Insertion Reaction: A Route to Highly Functionalized Vinylarenes

A straightforward method for the synthesis of highly functionalized vinylarenes through palladium‐catalyzed, norbornene‐mediated C?H activation/carbene migratory insertion is described. Extension to a one‐pot procedure is also developed. Furthermore, this method can also be used to generate polysubstituted bicyclic molecules. The reaction proceeds under mild conditions to give the products in satisfactory yields using readily available starting materials. This is a Catellani–Lautens reaction that incorporates different types of coupling partners. Additionally, this reaction is the first to demonstrate the possibility of combining Pd‐catalyzed insertion of diazo compounds and Pd‐catalyzed C?H activation.     

Visible‐Light‐Enabled Stereodivergent Synthesis of E‐ and Z‐Configured 1,4‐Dienes by Photoredox/Nickel Dual Catalysis

A stereodivergent reductive coupling reaction between allylic carbonates and vinyl triflates to furnish both E‐ and Z‐configured 1,4‐dienes has been achieved by visible‐light‐induced photoredox/nickel dual catalysis. The mild reaction conditions allow good compatibility of both vinyl triflates and allylic carbonates. Notably, the stereoselectivity of this synergistic cross‐electrophile coupling can be tuned by an appropriate photocatalyst with a suitable triplet‐state energy, providing a practical and stereodivergent means to alkene synthesis. Preliminary mechanistic studies shed some light on the coupling step as well as the control of the stereoselectivity step.     

Tandem Cross‐Coupling/Spirocyclization/Mannich‐Type Reactions of 3‐(2‐Isocyanoethyl)indoles with Diazo Compounds toward Polycyclic Spiroindolines

Tandem reactions of Pd‐catalyzed cross‐coupling of 3‐(2‐isocyanoethyl)indoles with diazoacetates and subsequent spirocyclization/Mannich‐type reaction have been developed to assemble polycyclic spiroindoline skeletons. Formation of spiroindolenines has been proven as the crucial step for the following Mannich‐type cyclization reaction. Accordingly, a novel approach on chiral phosphoric acid catalyzed Mannich‐type cyclization toward the formation of diastereomerically and enantiomerically enriched pentacyclic spiroindolines has been established. Moreover, the products of the reaction are versatile building blocks in synthetic chemistry, as demonstrated by the synthesis of the key framework of aspidosperma and kopsia alkaloids.     

A Visible Light Photocatalytic Cross‐Dehydrogenative Coupling/Dehydrogenation/6π‐Cyclization/Oxidation Cascade: Synthesis of 12‐Nitroindoloisoquinolines from 2‐Aryltetrahydroisoquinolines

A visible light‐induced photocatalytic dehydrogenation/6π‐cyclization/oxidation cascade converts 1‐(nitromethyl)‐2‐aryl‐1,2,3,4‐tetrahydroisoquinolines into novel 12‐nitro‐substituted tetracyclic indolo[2,1‐a]isoquinoline derivatives. Various photocatalysts promote the reaction in the presence of air and a base, the most efficient being 1‐aminoanthraquinone in combination with K₃PO₄. Further, the 12‐nitroindoloisoquinoline products can be accessed directly from C1‐unfunctionalized 2‐aryl‐1,2,3,4‐tetrahydroisoquinolines by extending the one‐pot protocol with a foregoing photocatalytic cross‐dehydrogenative coupling reaction, resulting in a quadruple cascade transformation.     

Palladium‐Initiated Radical Cascade Stereoselective Iodofluoroalkylation/Cycloisomerization of Ene‐vinylidenecyclopropanes

A novel and convenient palladium‐initiated radical cascade stereoselective iodofluoroalkylation/cycloisomerization of ene‐vinylidenecyclopropanes with fluoroalkyl iodides has been developed. The reaction proceeds under mild reaction conditions with high atom economy and stereoselectivity, thereby allowing an efficient access to a variety of difluoromethylated or perfluoroalkylated pyrrolidines tethered with an alkyl iodide. Two plausible radical pathways for the transformation have been proposed on the basis of the results of control experiments and previous reports, which in one case it was thought that palladium(0) was an initiator rather than a catalyst.     

Copper/Guanidine‐Catalyzed Asymmetric Alkynylation of Isatins

The highly enantioselective alkynylation of isatins, catalyzed by a bifunctional guanidine/CuI catalyst under mild reaction conditions, is described. The reaction is broad in scope with respect to alkyl/aryl‐substituted terminal alkynes and substituted isatins, thus affording bioactive propargylic alcohols in excellent yields and enantioselectivities.     

α‐ZrP/Uracil/Cu2+ nanoparticles as an efficient catalyst in the Morita‐Baylis‐Hillman reaction

A facile synthesis of uracil‐Cu²⁺ nanoparticles immobilized on alpha‐zirconium hydrogen phosphate (α‐ZrP), abbreviated as α‐ZrP/Uracil/Cu²⁺, was presented. This compound was synthesized by the thermal method and used as a reusable catalyst for the Morita‐Baylis‐Hillman reaction without any additives. First, (3‐ iodopropyl) trimethoxysilane as a linker is reacted with α‐ZrP support to give the α‐ZrP/IPTMOS. Addition of uracil and then the addition of copper (II) acetate to α‐ZrP/IPTMOS results in the production of selected catalyst. The Morita‐Baylis‐Hillman reaction catalyzed by α‐ZrP/Uracil/Cu^{2 +} demonstrated high product yield, short reaction time and a straightforward work‐up. The catalyst with enough outside surface was easily recovered using centrifugation and reused five times without a significant reduction in its activity.     

Iron‐catalyzed one‐pot oxidation/Knoevenagel condensation reaction using air as an oxidant

A green and highly efficient iron‐catalyzed one‐pot oxidation/Knoevenagel tandem reaction for the synthesis of α, β‐unsaturated nitriles from secondary alcohols and malononitrile has been achieved. The reaction performed under mild conditions with air as an oxidant, and provided the corresponding oxidation/Knoevenagel prudocts in good to excellent yields within short times avoiding the use of noble metal catalysts and bases. Remarkably, water is the only byproduct in this methodology. The reaction could be performed on a gram scale under the standard reaction conditions.     

The First One‐Pot,Solvent‐Free,Microwave‐Accelerated,Three‐Component Synthesis of Spirothiazolidin‐4‐ones via Staudinger/Aza‐Wittig Coupling/Cyclization

An efficient and rapid, solvent‐free, microwave‐accelerated, one‐pot, three‐component protocol for the synthesis of spirothiazolidin‐4‐ones from organic azides is reported for the first time via Staudinger/aza‐Wittig coupling/cyclization. The solvent‐free approach overcomes the limitations associated with the prevailing solution‐phase methodologies in the case of amines. In particular, its novelty is that it eradicates the vital limitation, i.e., the accumulation of H₂O (by‐product), which is known to affect the yield and rate of the reaction, thus affording the spirothiazolidin‐4‐ones in short reaction times in excellent yields.     

Introduction of Ag/CuO/MCM‐48 as an efficient catalyst for the one‐pot synthesis of novel pyran‐pyrrole hybrids

Bimetallic silver and copper incorporated mesoporous MCM‐48 (Ag/CuO/MCM‐48) was synthesized by simple wet‐impregnation method. The knowledge about its structural properties was gathered by means of Fourier transform‐infrared, energy‐dispersive X‐ray, X‐ray diffraction, field emission‐scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller analyses. The catalytic activity of Ag/CuO/MCM‐48 was examined in the one‐pot three‐component reaction of 3‐(1‐methyl‐1H‐pyrrol‐2‐yl)‐3‐oxopropanenitrile, malononitrile and various aromatic aldehydes leading to novel pyran‐pyrrole hybrid derivatives in reduced reaction times (5–10 min) and excellent yields (88–97%). Application of Ag/CuO/MCM‐48 as a potent heterogeneous catalyst with good reusability up to five times, use of ethanol as an eco‐compatible medium and chromatography‐free work‐up are some crucial green aspects of this procedure.     

Visible‐Light‐Induced Direct Photocatalytic Carboxylation of Indoles with CBr4/MeOH

Photocatalysis enables the cascade reactions of indoles and CBr₄ in MeOH through a C(sp²)?H functionalization/methanolysis sequence. The title reaction provides an efficient access to indole 2‐ and 3‐carboxylates in a single operation (no preinstallation of protecting as well as directing groups was required) with good yields under mild reaction conditions.     

The First Solvent‐Free,Microwave‐Accelerated,Three‐Component Synthesis of Thiazolidin‐4‐ones via One‐Pot Tandem Staudinger/aza‐Wittig Reaction

An efficient and rapid, solvent‐free, microwave‐accelerated, one‐pot, three‐component protocol for thiazolidin‐4‐ones synthesis from organic azides has been reported for the first time via Staudinger/aza‐Wittig reaction. The microwave‐accelerated, solvent‐free approach overcomes the limitations associated with the prevailing solution phase methodologies. In particular, its novelty is that it eradicates the vital limitation, that is, accumulation of water (byproduct) that is known to affect the yield and rate of the reaction. Thus, a library of thiazolidin‐4‐ones has been synthesized in short time in excellent yields (92–96%).     

Tandem Hydroformylation/Reductive Amination of 3‐Allyl‐2‐methylquinazolin‐4(3H)‐one

The 3‐allyl‐2‐methylquinazolin‐4(3H)‐one ( 1 ), a model functionalized terminal olefin, was submitted to hydroformylation and reductive amination under optimized reaction conditions. The catalytic carbonylation of 1 in the presence of Rh catalysts complexed with phosphorus ligands under different reaction conditions afforded a mixture of 2‐methyl‐4‐oxoquinazoline‐3(4H)‐butanal ( 2 ) and α,2‐dimethyl‐4‐oxoquinazoline‐3(4H)‐propanal ( 3 ) as products of ‘linear’ and ‘branched’ hydroformylation, respectively (Scheme 2). The hydroaminomethylation of quinazolinone 1 with arylhydrazine derivatives gave the expected mixture of [(arylhydrazinyl)alkyl]quinazolinones 5 and 6 , besides a small amount of 2 and 3 (Scheme 3). The tandem hydroformylation/reductive amination reaction of 1 with different amines gave the quinazolinone derivatives 7 – 10 . Compound 10 was used to prepare the chalcones 11a and 11b and pyrazoloquinazolinones 12a and 12b (Scheme 4).     

A facile one‐pot synthesis of novel substituted 1,2,3,4‐tetrahydropyrimidine,part 2: Synthesis of 1‐(aralkyl/aryl)‐3‐(alkyl/aralkyl/aryl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines

1‐(Aralkyl/aryl)‐3‐(alkyyaralkyl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines ( 2a‐c ) have been synthesized by dethiomethylation of 5‐aroyl‐6‐methylthio‐1,2,3,4‐tetrahydropyrimidines ( 1a‐c ). An alternative one‐pot synthetic strategy has been developed for the title compounds 2a‐t by the reaction of enaminones 3 with pri mary amine and formaldehyde in refluxing methanol in good yields.     

Silicon‐grafted Ag/AgX/rGO nanomaterials (X = Cl or Br) as dip‐photocatalysts for highly efficient p‐nitrophenol reduction and paracetamol production

In this work, plasmonic Ag/AgX/rGO (X = Cl or Br) nano‐photocatalysts were grafted with silicon by adding trimethylsilyl chloride as silicon precursor. The synthesized Ag/AgX/rGO‐Si hybrids showed a large improvement of photocatalytic activity towards the synthesis of p‐aminophenol (PAP) as well as paracetamol (acetaminophen; APAP) through the photoreduction of p‐nitrophenol (PNP). The prepared catalysts Ag/AgX/rGO were characterized using SEM, XRD, FTIR and the reduction reaction of p‐nitrophenol was monitored by UV–Vis measurements, GC/MS and ¹HNMR data. From the results, it was demonstrated that the rate order of reduction process of the PNP to PAP and to APAP under visible light irradiation of the samples was as follows; Ag/AgBr/rGO‐Si > Ag/AgCl/rGO‐Si > Ag/AgBr/rGO > Ag/AgCl/rGO. The reaction mechanism had been postulated that was supported with the spectroscopic data. In addition, the catalysts were recovered from the reaction medium and re‐used in three cycles that indicated the reusability and stability of the catalysts. This study was featured by the following; i) fast reaction, ii) the reduction of p‐nitrophenol to paracetamol was performed in a facile one‐pot reaction compared to previous approaches that tends to reduce the production cost, and iii) investigations on the catalytic properties of Ag/AgX/rGO in organic transformations open the door to find a benefice of these catalysts in other organic reactions and in the development in the synthesis of pharmaceutical products.     

Atom transfer radical polymerization of n‐butyl acrylate catalyzed by CuBr/N‐(n‐hexyl)‐2‐pyridylmethanimine

The homogeneous atom transfer radical polymerization (ATRP) of n‐butyl acrylate with CuBr/N‐(n‐hexyl)‐2‐pyridylmethanimine as a catalyst and ethyl 2‐bromoisobutyrate as an initiator was investigated. The kinetic plots of ln([M]₀/[M]) versus the reaction time for the ATRP systems in different solvents such as toluene, anisole, N,N‐dimethylformamide, and 1‐butanol were linear throughout the reactions, and the experimental molecular weights increased linearly with increasing monomer conversion and were very close to the theoretical values. These, together with the relatively narrow molecular weight distributions (polydispersity index ～ 1.40 in most cases with monomer conversion > 50%), indicated that the polymerization was living and controlled. Toluene appeared to be the best solvent for the studied ATRP system in terms of the polymerization rate and molecular weight distribution among the solvents used. The polymerization showed zero order with respect to both the initiator and the catalyst, probably because of the presence of a self‐regulation process at the beginning of the reaction. The reaction temperature had a positive effect on the polymerization rate, and the optimum reaction temperature was found to be 100 °C. An apparent enthalpy of activation of 81.2 kJ/mol was determined for the ATRP of n‐butyl acrylate, corresponding to an enthalpy of equilibrium of 63.6 kJ/mol. An apparent enthalpy of activation of 52.8 kJ/mol was also obtained for the ATRP of methyl methacrylate under similar reaction conditions. Moreover, the CuBr/N‐(n‐hexyl)‐2‐pyridylmethanimine‐based system was proven to be applicable to living block copolymerization and living random copolymerization of n‐butyl acrylate with methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3549–3561, 2002     

Visible‐Light Photoredox‐Catalyzed C−H Difluoroalkylation of Hydrazones through an Aminyl Radical/Polar Mechanism

An unprecedented visible‐light‐induced direct C?H bond difluoroalkylation of aldehyde‐derived hydrazones was developed. This reaction represents a new way to synthesize substituted hydrazones. The salient features of this reaction include difluorinated hydrazone synthesis rather than classical amine synthesis, extremely mild reaction conditions, high efficiency, wide substrate scope, ease in further transformations of the products, and one‐pot syntheses. Mechanistic analyses and theoretical calculations indicate that this reaction is enabled by a novel aminyl radical/polar crossover mechanism, with the aminyl radical being oxidized into the corresponding aminyl cation through a single electron transfer (SET) process.     

Synthesis of novel N‐alkyl/aryl‐N′‐(4‐arylthiazol‐2‐yl)‐N″‐xylosyl guanidines

The reaction of 2,3,4‐tri‐O‐acetyl‐β‐D‐xylopyranosyl isothiocyanate ( 1 ) and 2‐amino‐4‐arylthiazoles ( 2 ) gave xylosylthioureas 3 . These thiourea derivatives reacted with alkyl/aryl amine in the presence of HgCl₂ to give a new series of N‐alkyl/aryl‐N″‐(4‐arylthiazol‐2‐yl)‐N″‐xylosyl guanidines 4 . Some of the synthesized guanidines were screened for their biological activity. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:688–694, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20379