Cycloaddition reactions of heterocyclic azides with 2-cyanoacetamidines as a new route to C,N-diheteroarylcarbamidines

A novel and efficient base-catalyzed, transition-metal-free method for the synthesis of diheterocyclic compounds connected by an amidine linker, including apart from the common 1,2,3-triazole ring, either an additional pyrimidinedione, 4-nitroimidazole, isoxazole, 1,3,4-triazole, 2-oxochromone or thiazole ring, has been developed. The process was facilitated by a strong base and includes the cycloaddition reaction of 3,3-diaminoacrylonitriles (2-cyanoacetamidines) to heterocyclic azides followed by a Cornforth-type rearrangement to the final products. The reaction is tolerant to various N-monosubstituted 3,3-diaminoacrylonitriles and to different heterocyclic azides. The developed method has a broad scope and can be applied to obtain a variety of N-heteroaryl-1,2,3-triazole-4-carbimidamides with alkyl, allyl, propargyl, benzyl, cycloalkyl, and indolyl substituents at the N1 position .

Visible-light-induced dehydrogenative amidation of aldehydes enabled by iron salts

A direct dehydrogenative amidation reaction of aldehydes and amines under a visible light mediated ligand-to-metal charge transfer (LMCT) process was described. In this protocol, aldehyde substrates were activated by photoinduced hydrogen atom abstraction (HAA), generating acyl chloride intermediates followed by nucleophilic addition of amines. The synthetic method furnishes good functional group tolerance and broad substrate scope toward both aliphatic and aromatic components.

Recent advances in nanoparticles towards sustainability and their application in organic transformations in aqueous media

Nanoparticles (NPs) play a crucial role in organic transformation and are becoming increasingly attractive in the field of catalysis as they show good catalytic activity in organic as well as aqueous media. Numerous NPs have been utilized for several organic transformations in aqueous media, which have led to dedicated efforts for the complete coverage of the application of metal, metal oxide, bimetallic and supported NPs in water-mediated organic transformations in the last decades. This review aims to provide current highlights on the application of various types of metal NPs for organic transformations in aqueous media. The remarkable benefits associated with the catalytic application of NPs in water allows for various transformations to be performed under very mild and green conditions. Lastly, the author's perspectives are briefly considered, including future developments and crucial challenges in the ever-growing field of nanocatalysis.

Switchable aqueous catalytic systems for organic transformations

In living organisms, enzyme catalysis takes place in aqueous media with extraordinary spatiotemporal control and precision. The mechanistic knowledge of enzyme catalysis and related approaches of creating a suitable microenvironment for efficient chemical transformations have been an important source of inspiration for the design of biomimetic artificial catalysts. However, in "nature-like" environments, it has proven difficult for artificial catalysts to promote effective chemical transformations. Besides, control over reaction rate and selectivity are important for smart application purposes. These can be achieved via incorporation of stimuli-responsive features into the structure of smart catalytic systems. Here, we summarize such catalytic systems whose activity can be switched 'on' or 'off' by the application of stimuli in aqueous environments. We describe the switchable catalytic systems capable of performing organic transformations with classification in accordance to the stimulating agent. Switchable catalytic activity in aqueous environments provides new possibilities for the development of smart materials for biomedicine and chemical biology. Moreover, engineering of aqueous catalytic systems can be expected to grow in the coming years with a further broadening of its application to diverse fields.

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)-promoted reduction of azides to amines under metal-free conditions

A simple and novel metal-free reduction of azides to amines in the presence of DBU is reported. This DBU-promoted transformation features good functional group tolerance and high chemo-selectivity.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

A Highly Efficient Ga(OTf)3/KI-Catalysed Transformation of aryl azides to aryl amines using low catalyst loading

A highly proficient transformation of aryl azides to aryl amines under Ga(OTf)3/KI catalysis is described.

Au nanoparticle@hollow mesoporous carbon with FeCo/graphitic shell nanoparticls as a magnetically recyclable yolk-shell nanocatalyst for catalytic reduction of nitroaromatics

We have developed a highly stable and magnetically recyclable yolk–shell nanocatalyst for catalytic reduction of nitroaromatics. This nanocatalyst is composed of a ~13 nm Au nanoparticle encapsulated in a hollow mesoporous carbon (hmC) shell with a diameter of ~120 nm and a thickness of ~15 nm. The hmC shell contains ~6 nm FeCo/graphitic carbon shell (FeCo/GC) nanoparticles. We have synthesized the Au@hmC-FeCo/GC nanocatalyst by thermal decomposition of Fe and Co precursors in silica of a solid core/mesoporous shell structure containing a Au nanoparticle within the core, subsequent ethylene chemical vapor deposition (CVD), and then removal of the silica by treatment with aqueous HF. The Au@hmC-FeCo/GC has superparamagnetism and high saturation magnetization (29.2 emu g⁻¹) at room temperature. It also shows a type IV sorption isotherm, typical for mesoporous carbon (pore diameter = 3.5 nm), thereby ensuring ready accessibility to the Au core by substrates. We have shown that the Au@hmC-FeCo/GC catalyses the reduction of 4-nitrophenol and 4-nitrotoluene more efficiently than Au nanoparticles do, can be separated very quickly from the reaction mixture using an magnet, and can be reused for the same reduction reaction at least five times without loss of the initial level of catalytic activity.

An efficient copper-based magnetic nanocatalyst for the fixation of carbon dioxide at atmospheric pressure

In the last few decades, the emission of carbon dioxide (CO2) in the environment has caused havoc across the globe. One of the most promising strategies for fixation of CO2 is the cycloaddition reaction between epoxides and CO2 to produce cyclic carbonates. For the first time, we have fabricated copper-based magnetic nanocatalyst and have applied for the CO2 fixation. The prepared catalyst was thoroughly characterized using various techniques including XRD, FT-IR, TEM, FE-SEM, XPS, VSM, ICP-OES and elemental mapping. The reactions proceeded at atmospheric pressure, relatively lower temperature, short reaction time, solvent- less and organic halide free reaction conditions. Additionally, the ease of recovery through an external magnet, reusability of the catalyst and excellent yields of the obtained cyclic carbonates make the present protocol practical and sustainable.

Visible-light-driven Efficient Photocatalytic Reduction of Organic Azides to Amines over CdS Sheet-rGO Nanocomposite

CdS sheet-rGO nanocomposite as a heterogeneous photocatalyst enables visible-light-induced photocatalytic reduction of aromatic, heteroaromatic, aliphatic and sulfonyl azides to the corresponding amines using hydrazine hydrate as a reductant. The reaction shows excellent conversion and chemoselectivity towards the formation of the amine without self-photoactivated azo compounds. In the adopted strategy, CdS not only accelerates the formation of nitrene through photoactivation of azide but also enhances the decomposition of azide to a certain extent, which entirely suppressed formation of the azo compound. The developed CdS sheet-rGO nanocomposite catalyst is very active, providing excellent results under irradiation with a 40 W simple household CFL lamp.

Controllable synthesis of a Pd/PdO nanocomposite as a catalyst for hydrogenation of nitroarenes to anilines in water

The different Pd/PdO ratios nanoparticles supported on oxide carbon nanotubes can be controllable synthesized by a one-pot gas–liquid interfacial plasma method, which can catalyze the hydrogenation of nitroarenes in water by atmosphere pressure H₂.

Selectivity and activity in catalytic hydrogenation of azido groups over Pd nanoparticles on aluminum oxy-hydroxide

A practical and effective catalytic method has been developed for the reduction of aryl azides in the presence of PdAlO(OH) nanoparticles and sodium borohydride.