NH4I-promoted N-acylation of amines via the transamidation of DMF and DMA under metal-free conditions

An unprecedented NH₄I-promoted N-formylation and N-acetylization of various amines with dimethylformamide (DMF) and dimethylacetamide (DMA) has been developed. This protocol shows broad substrate scope for aromatic, aliphatic, and heterocyclic amines, which provides a metal-free strategy for N-acylation featuring mild reaction conditions, as well as inexpensive and readily available starting materials.     

Copper-catalyzed denitrogenative N-arylation of sulfoximines and sulfonamides with arylhydrazines

A Cu-mediated ligand-free arylation of NH-sulfoximines and sulfonamides by arylhydrazine hydrochlorides was herein demonstrated. The oxidative transformation provided an easy access towards N-aryl sulfoximines and sulfonamides in high yields (up to 93% yields) with broad functional groups tolerance (up to 36 examples). The protocol was proposed to take place through the free radical pathway based on the results of control reactions and EPR analysis.     

Fe-exchanged clay catalyzed transamidation of amides with amines under solvent-free condition

Fe³⁺-exchanged montmorillonite is shown to be an effective and reusable heterogeneous catalyst for the transamidation of various amides and amines under solvent-free condition. The catalyst shows high yields and wide substrate scope.     

Base catalyzed intramolecular transamidation of 2-aminoquinazoline derivatives on solid phase

A novel intramolecular cyclo-elimination via transamidation on the Rink Amide AM resin under mild basic conditions is presented. The methodology led to the synthesis of an important class of cardiotonic agents: imdiazo- and pyrimido-quinazolines from the corresponding 2-aminoquinazoline hydrobromide salt under mild basic conditions. NMR based titration studies revealed the role of hydrobromide as a molecular switch, which on removal triggers the cyclisation of aminoquinazoline to tricyclic structures. The main advantage of transamidation under basic conditions over the TFA cleavage is the recyclability of the resin obtained after cyclo-elimination. This has been demonstrated by successive synthesis of four structurally diverse imidazoquianzolin-2-ones using the same batch of resin without any cross contamination.     

Graphene oxide (GO) catalyzed transamidation of aliphatic amides: An efficient metal-free procedure

Transamidation involves direct interconversion of an amide with amine, and represents an alternative to the common method of amide formation from the reaction of carboxylic acid with an amine. While the carboxamides have huge potential in biological systems and polymer industries, their formation from carboxylic acids requires activation by a suitable catalyst. A metal-free transamidation of aliphatic amide with aromatic amine catalyzed by graphene oxide (GO) has been developed and established as a general, synthetically useful and selective procedure. Graphene oxide bearing several carboxylic acids on the edges and having large surface area acts as an efficient and recyclable catalyst for transamidation.     

Stereocontrolled synthesis of bicyclic ureas and sulfamides via Pd-catalyzed alkene carboamination reactions

The synthesis of bicyclic ureas and sulfamides via palladium-catalyzed alkene carboamination reactions between aryl/alkenyl halides/triflates and alkenes bearing pendant cyclic sulfamides and ureas is described. The substrates for these reactions are generated in 3–5 steps from commercially available materials, and products are obtained in good yield with up to >20:1 diastereoselectivity. The stereochemical outcome of the sulfamide alkene addition is consistent with a mechanism involving anti-aminopalladation of the alkene, whereas the stereochemical outcome of the urea alkene addition is consistent with a syn-aminopalladation mechanism.     

Nucleophile induced ligand rearrangement reactions of alkoxy- and arylsilanes

The ligand-redistribution reactions of aryl- and alkoxy-hydrosilanes can potentially cause the formation of gaseous hydrosilanes, which are flammable and pyrophoric. The ability of generic nucleophiles to initiate the ligand-redistribution reaction of commonly used hydrosilane reagents was investigated, alongside methods to hinder and halt the formation of hazardous hydrosilanes. Our results show that the ligand-redistribution reaction can be completely inhibited by common electrophiles and first-row transition metal pre-catalysts.     

Microwave-assisted heteropolyanion-based ionic liquids catalyzed transamidation of non-activated carboxamides with amines under solvent-free conditions

An environmentally benign and highly efficient protocol for the transamidation of non-activated carboxamides with amines using heteropolyanion-based ionic liquids as catalysts under microwave-assisted and solvent-free conditions has been developed. As evaluated by the reactions of a structurally diverse set of amides and amines, the scope and utility of the transamidation proved to be quite general. Operational simplicity, solvent-free media, the potential reusability of catalysts and wide functional group tolerance are attractive features. This method provides a much improved protocol over the existing methods.     

Novel reactions of ninhydrin oxime with mercaptoalkanoic acids

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Non-covalent interactions in stoichiometric and catalytic reactions of iridium pincer complexes

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Enzyme-mediated oxidative dimerization reactions of cyano-resveratrol analogues

The synthesis and oxidative coupling reactions of two cyano-resveratrol analogues were studied. An 8-5-coupled dihydrobenzofuran-type dimer and an 8-8-coupled diastereoisomeric indane mixture were prepared. The cyano groups of the resveratrol analogues had almost no influence on the regio- or stereoselectivity of the coupling reactions of the two precursors.     

BF3-promoted reactions between aryl aldehydes and 3-diazoindolin-2-imines: Access to 2-amino-3-arylindoles

An efficient and highly regioselective synthesis of 2-amino-3-arylindoles via the BF₃-promoted reaction of 3-diazoindolin-2-imines with aryl aldehydes is described. This reaction could be carried out under mild reaction conditions with a broad scope of substrates. Moreover, the operation is of practical usage and could be scaled up.     

Advances on asymmetric organocatalytic 1,4-conjugate addition reactions in aqueous and semi-aqueous media

Asymmetric Michael addition reactions or 1,4-conjugate addition reactions are considered to be the fundamental C–C bond-forming reaction for the construction of chiral β-nitro, β-carbonyl and several other important structural motifs in organic synthesis. After the development of many chiral metal complexes as catalysts, a tremendous growth in the design and applications of variety of new chiral organocatalysts for asymmetric 1,4-conjugate addition reactions has been witnessed over the last two decades. Initially, asymmetric organocatalysis has been performed in organic solvents, but gradually performing the same catalysis in aqueous and semi-aqueous media became a necessity due to environmental aspects as well as to achieve better reactivity and selectivity. The structural and functional diversity of the chiral organocatalysts derived from natural and synthetic sources utilized differently the water either as the sole solvent, co-solvent or additive for optimising their best performances. In the present review, we discuss a detailed and comprehensive report on the advancement in the field of asymmetric organocatalytic 1,4-conjugate addition reactions in aqueous and semi-aqueous media.     

Solvent-free Suzuki and Stille cross-coupling reactions of 4- and 5-halo-1,2,3-triazoles

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Reactive sensing of gold (III) by coumarin tethered fluorescent probe through alkyne activation

A novel strategy, involving anchoring and un-anchoring of coumarin based fluorophore, has been established for the selective detection of Au³⁺ species. Selective sensing of Gold (Au³⁺) was triggered due to alkynophilicity of gold ions to create lateral fluorescence of a latent fluorophore. The 4-methyl-2-oxo-2H-chromen-7-yl 2-(2-phenylethynyl) benzoate (CEB) probe was synthesized by reacting 7-hydroxy-4-methylcoumarin with iodo-benzoic acid. CEB probe has an absorption at 300 nm and 335 nm which decreases gradually and new absorption appeared at 406 nm due to Au³⁺ promoted ester hydrolysis selectively over other metal ions with great sensitivity, which accompanies a turn on fluorescence change produced by 7-hydroxy coumarin. The principle behind this sensing strategy is activation of triple bond induced uniquely by Au⁺³ ions leading to cascade and delivers active fluorophore. The sensing mechanism was proposed and supported by ¹H NMR, MS and TD-DFT experiments. The density functional theory (DFT) and time dependent density functional theory (TD-DFT) theoretical results of the CEB-probe and Au³⁺ reaction is in good agreement with the experimental results. Additionally, probe could be well incorporated onto the test strips for effective detection of Au^3+.     

Oxidative reactions of sulfinyl dienes as an entry to functionalized carbohydrate-like products and furans

Oxidative cleavage (OsO₄/NaIO₄) of a monoprotected dihydroxy sulfinyl diene affords a lactol, readily transformed into a sulfinyl pyranose. Alternatively, base promoted intramolecular cyclization of a lactol derived carbamate to a bicyclic oxazolidinone followed by simple transformations leads to an amino sulfonyl pyranose. In contrast, ozonolysis of a variety of hydroxy sulfinyl dienes leads to fair yields of 3-sulfinyl furans in a single step.     

Preparation and characterization of NiFe bimetallic micro-particles and its composite with silica shell

Magnetic NiFe particles were synthesized through hydrothermal method using hydrazine as reductant. Composite particles with core-shell structure were further achieved by depositing silicon dioxide generated via carbonation decomposition of sodium silicate solution on the surface of magnetic cores. Characterized by XRD, the Ni₉Fe particles are of fcc-type structure, and the structure of magnetic cores in composite particles was maintained despite being covered by SiO₂ shell. The existence of SiO₂ shells in the composite particles were demonstrated by SEM, EDS and IR. The results from TG and VSM indicated that the shell structure affected the physiochemical properties. The composite particles exhibited remarkable resistance to oxidation in comparison with Ni₉Fe particles due to being protected by SiO₂ shell. Meanwhile, both of them are soft magnetic materials, but Ms, Mr and Hc in Ni₉[email protected]₂ particle decreased compared with magnetic NiFe particles. The formation mechanisms of Ni₉Fe micro-particles and composite Ni₉Fe particles were discussed.     

Enantioselective reactions catalyzed by phosphine oxides

The development of chiral small organic molecules that serve as Lewis base catalysts promoting highly stereoselective transformations has been the subject of intense research over the past decades. As a matter of fact, among the plethora of molecules used as Lewis bases, chiral phosphine oxides have thoroughly been overlooked by the organic synthetic community. Thus, this review focuses exclusively on Lewis base catalysis mediated by chiral phosphine oxides with emphasis on mechanistic aspects, covering most of the publications related to this field since their first use as organocatalyst in 2005 until the end of March 2019.     

Guanidine organocatalysis for enantioselective carbon-heteroatom bond-forming reactions

Guanidine-containing molecules have been employed as organocatalysts, and chiral guanidines have been widely explored as catalysts for mediating asymmetric reactions by constructing an asymmetric reaction environment. Currently, many guanidine-catalyzed asymmetric reactions are available, and some excellent reviews have appeared. In this Digest, we focused on recent progress in the guanidine-catalyzed asymmetric construction of CN, CO, CP, and CS bonds, especially developments since 2010.     

Importance of thorough conformational analysis in modelling transition metal-mediated reactions: Case studies on pincer complexes containing phosphine groups

Advances in processing capabilities of computer clusters have allowed for the full modeling of organometallic complexes that previously would have been simplified to reduce computational cost. Increased feasibility of computational modeling offers new challenges, not only in terms of limitations of methods and theory, but attention should be paid to complexes that can exist in many conformations, as the appropriate choice of conformer may be easily overlooked. In this work a series of pincer complexes with isopropyl and cyclopentyl substituents have been chosen as examples to demonstrate the importance of conformational analysis. The complexes examined contain four isopropyl or cyclopentyl groups on phosphor atoms generating between 27 and 324 possible rotamers. The importance of conformational search in a mechanistic investigation is demonstrated with the CO₂ insertion into a nickel hydride bond of POCOP ⁱPr nickel hydride complex. Results show that the reaction energy profile can be both exergonic and endergonic depending on rotamer choice. Specifically, the POCOP^iPr Ni-formato complex product of the CO₂ insertion reaction had an energy difference between the lowest and highest energy rotamer as high as 16.8 kcal/mol. The significant energy differences between rotamers highlight the importance of thorough conformational analysis and should be taken into consideration when evaluating the energy profile of related reactions.