ArCH(OMe)₂--a Pt(IV)-catalyst originator for diverse annulation catalysis

FeCl3/SiO2-catalyzed bis-indolylation of acetals and ketals: a highly atom-economical approach to the selective deprotection of protected carbohydrates

A simple and green catalytic system is developed for the synthesis of 3,3'-bisindolyl(methanes) (BIMs) using cyclic/acyclic acetals as the carbon source for the bridging residue between two indole motifs. The reaction occurred under mild and benign conditions using FeCl3/SiO2 as a heterogeneous catalyst without the requirement of any toxic organic solvents. The ready availability and recyclability of the catalytic system allows the reaction to be highly efficient, resulting in very good BIM products. DFT studies were also performed to establish the proposed mechanism and preferential formation of unsymmetrical bisindolylmethanes using equimolar amounts of different indoles. The present protocol is also extended to the bisindolylation-induced selective cleavage of protected carbohydrates to diols in a 100% carbon-preservation and maximized atom-economical manner.

An elegant approach for the synthesis of multisubstituted imidazole via FeCl3/SiO2 catalyzed activation of acetals: a photophysical study of an imidazole-carbazole hybrid

A simple and solvent-free catalytic system was developed for the direct conversion of multisubstituted imidazoles through the reaction of acetals and benzils with ammonium acetate/amines as the source of nitrogen. The reaction occurred under mild and benign conditions using FeCl3/SiO2 as a heterogeneous catalyst without the requirement of any toxic organic solvents. The easy preparation and recyclability of the catalyst allows the reaction to be simple and highly efficient, resulting in very good yields of imidazoles. Novel imidazole-carbazole hybrid compounds were also synthesised by adopting the present methodology. Single crystal X-ray diffraction study indicated the presence of a CH⋯π supramolecular interaction that renders effective molecular packing in the solid state. The steady-state and spectro-dynamic behaviours of these hybrid molecules were investigated, and it was revealed that a solvent-dependent excimer-coupled ICT phenomenon guided excited state photophysics. Very unusual excimer lifetime was noticed in the solid state of this bis-heterocyclic compound owing to the stacking of molecules via CH⋯π interaction, as evident from the X-ray studies.

Gold(I)-catalyzed synthesis of N-alkenyl 2-pyridonyl sec-amines

N-Alkenyl 2-pyridonyl amines are afforded in high yields via a gold-catalyzed rearrangement of 2-propargyloxypyridine and 2-(but-3-yn-1-yloxy)pyridine under acidic conditions. This approach exhibits significant utility due to its outstanding efficiency of conversion in the synthesis of secondary amines as a one-pot reaction. The initial step of the method involves a cyclization reaction for the production of pyridinium salts, followed by the next stage, where rearrangement is accomplished through the nucleophilic addition phenomenon. This approach provides the conversion of primary amines into secondary amines, resulting in a single product. Furthermore, the methodology presents a high degree of tolerance towards several pyridine and aniline derivatives, resulting in the formation of products with excellent yields.

Photocatalytic Generation of Nitrenes for Rapid Diaziridination

A blue LED, an organic photocatalyst (rose bengal), and the Lewis acid like oxidant PhI(OAc)₂ were utilized to generate nitrene intermediates through reactions of 1,2-diols and aliphatic amines under mild reaction conditions. A versatile and rapid diaziridination strategy was established to construct functionalized 1,2-disubstituted diaziridines, diaziridines with chiral substituents, and 1,2,3-trisubstituted analogues with excellent reaction rates, yields, and stereoselectivities. Control and labeling experiments to elucidate the mechanism of this elegant metal-free photocatalyzed cyclization reaction were performed.

PdII-Catalyzed Oxidative Aldehyde-sp2C-H Functionalization and Cyclization Using NHC with Mild Oxidant DMSO for the Selective Synthesis of Esters, Sugar-Based Analogues, and β-Hydroxy Chromanones: An 18O-Labeling Study

We assume formation of acyl-Pd^II-N-heterocyclic-carbene (NHC) organometalics for diverse C-O/O-C and C-C/C-O coupling catalysis of direct functionalization and cyclization reactions. We report the first use of dimethyl sulfoxide (DMSO) as an oxidant under an inert atmosphere to O₂-sensitive NHC for oxidative transformations. In situ generated imidazolium halides are utilized as a precursor of NHC and as a source of alkyl group for the sp²C-H functionalization of aldehydes to esters under mild conditions. In contrast to the reported NHC-catalyzed esterification strategies, the outstanding substrate scope of this mild catalysis approach is established through synthesis of thermally labile sugar-based chiral esters. Our competition experiments using various unsymmetrical imidazolium halides revealed an ascending rate of migratory aptitude among methyl ≪ allyl < crotyl < cinnamyl < benzyl moiety. DMSO is used as an oxidant for both esterification and cyclization reactions, and the transfer of the DMSO-oxygen to ester is confirmed using an ¹⁸O-labeling experiment. The diverse activity using DMSO-oxygen to acyl-Pd^II-NHC is verified by developing a unique C-C-coupled cyclization with side-chain hydroxylation of olefin to achieve valuable β-hydroxy chromanones.

Functionalised Mn(VI)-nanoparticles: an advanced high-valent magnetic catalyst

We discover Mn(VI)-nanoparticles (NPs) bearing functional groups, high oxidation state, strong electron affinity, unique redox and paramagnetic nature, which opens up a new avenue to catalysis, magnetism and material application. However, its synthesis is challenging and remains unexplored because of associated serious difficulties. A simple benign synthetic strategy is devised to fabricate the high-valent NPs using mild reducing agent bromide, which transformed Mn(VII) to valuable Mn(VI)-species. The EELS-imaging of individual elements, ESI-MS, XPS and other techniques established its composition as Br(Me3SiO)Mn(VI)O2. It revealed significantly improved magnetic moment (SQUID) with isotropic hyperfine splitting of six line spectrum (EPR). The high-oxidation state and incorporated-ligands of the metals present on the active surface of the NPs led to development of a general catalytic process for oxidative heterodifunctionalisation to C-C triple bond towards formation of a new O-C/N-C/S-C and C-C coupling cum cyclisation to biologically important flavones and their aza- and marcapto-analogues, and valuable enaloxy synthons.

Fabrication of Mn2O3 nanorods: an efficient catalyst for selective transformation of alcohols to aldehydes

Self-assembled high surface area Mn₂O₃ nanorods have been fabricated through an effective polymer–surfactant interaction and their outstanding catalytic property for the selective transformation of alcohols to aldehydes has been discovered.

General solvent-free ionic liquid catalyzed C–N/C–C coupled cyclization to diverse dihydropyrimidinones and new organic materials: Langmuir–Blodgett film study

An ionic liquid catalyzed dual C–N/C–C coupled cyclization under solvent-free green conditions to DHPMs and their innovative new organic materials by LB film study are demonstrated.

Synthesis and diverse general oxidative cyclization catalysis of high-valent MoVIO2(HL) to ubiquitous heterocycles and their chiral analogues with high selectivity

The first synthesis and diverse oxidative cyclization catalysis properties of high-valent Mo^VI–triazole are demonstrated towards highly selective construction of benzimidazoles, benzothiazoles, isoxazolines, isoxazoles and their chiral analogues.

Ni(0)–Cu(i): a powerful combo catalyst for simultaneous coupling and cleavage of the C–N bond with cyclization to valuable amide-based pyrroles and 4-pyridones

We demonstrate unprecedented Ni(0)–Cu(i) combo catalysis for sequential bond activated domino N–C/C–C coupled annulation with N–C bond cleavage to afford valuable amide-based polysubstituted pyrroles and 4-pyridones selectively from β-ketoanilides.

General base-tuned unorthodox synthesis of amides and ketoesters with water

We discovered a highly reactive λ³-hypervalent iodane species using an inorganic/organic base for the unorthodox synthesis of amides and ketoesters through grafting terminal alkynes. In contrast to the metal-catalyzed dehydrative approaches the in situ generated nonmetallic reagent efficiently created C–N/C–O and CO bonds with amines/alkynes and water at rt.

Ni(ii)–salt catalyzed activation of primary amine-sp3Cα–H and cyclization with 1,2-diketone to tetrasubstituted imidazoles

NiCl₂·6H₂O and Ni(OAc)₂·4H₂O were found as efficient catalysts for C–H activation of benzyl and aliphatic amines for an unprecedented multi C–N bond forming cyclization with 1,2-diketones under refluxing toluene to furnish highly substituted and polycyclic imidazoles.