Solvent-Free Syntheses of 1,5-Benzodiazepines Using HY Zeolite as a Green Solid Acid Catalyst

1,5-Benzodiazepines are synthesized from 1,2-diamines and ketones catalyzed by HY zeolite at 50 °C under solvent-free conditions. This process offers an easy and efficient synthesis of substituted 1,5-benzodiazepines in high yields. The advantages of this protocol are operational simplicity, nontoxicity, low cost, easy recovery, and an environmentally benign nature. The catalyst is recovered by filtration and reused six times without significant loss in its catalytic activity. A plausible mechanism is also proposed

Copper(I)‑Y Zeolite-Catalyzed Regio- and Stereoselective [2 + 2 + 2] Cyclotrimerization Cascade: An Atom- and Step-Economical Synthesis of Pyrimido[1,6‑<i>a</i>]quinoline

An elegant copper­(I)-Y zeolite-catalyzed tandem process, involving ketenimine-based termolecular [2 + 2 + 2]/[NC + CC + NC] cycloaddition, using sulfonyl azide, alkyne, and quinoline, to prepare pyrimido­[1,6-<i>a</i>]­quinolines is reported. In this straightforward, highly atom- and step-economical protocol, copper­(I) promotes for azide–alkyne [3 + 2] cycloaddition which is followed by ring-rearrangement/ketenimine formation/regio- and stereoselective [2 + 2 + 2] termolecular cycloaddition and dehydrogenation cascade to yield selectively the <i>E</i>-isomer of pyrimido­[1,6-<i>a</i>]­quinoline

Copper(I)-Catalyzed Three Component Reaction of Sulfonyl Azide, Alkyne, and Nitrone Cycloaddition/Rearrangement Cascades: A Novel One-Step Synthesis of Imidazolidin-4-ones

A novel one-pot azide–alkyne/ketenimine–nitrone cycloaddition sequence that is induced by copper(I) and allows the transformation of sulfonyl azides, alkynes, and nitrones to highly substituted imidazolidin-4-ones is described. The corresponding heterogeneous version utilizing Cu(I)-modified zeolites as recyclable heterogeneous catalysts shows marginally improved yield and diastereoselectivity

One-Pot Synthesis of Propargylamines Using Ag(I)-Exchanged K10 Montmorillonite Clay as Reusable Catalyst in Water

Ag­(I)-exchanged K10 montmorillonite clay is found to be an efficient heterogeneous catalyst for the one-pot three-component coupling of terminal alkynes, amines, and aqueous formaldehyde (A³ coupling) to yield corresponding propargylamines in water. In all the cases, quantitative yields of the desired products are obtained. The catalyst is recovered by filtration and reused several times with only a slight decrease in its catalytic activity. This atom economical methodology does not require an additional co-catalyst or activator, and water is the only byproduct. Interestingly, the reaction can also be performed under solvent-free conditions in the case of aromatic and aliphatic aldehydes, along with formaldehyde, affording propargylamine derivatives in higher yields. A tentative mechanism is also proposed for this transformation

One-Pot Multicomponent Solvent-Free Synthesis of 2‑Amino‑4<i>H</i>‑benzo[<i>b</i>]pyrans Catalyzed by Per-6-amino-β-cyclodextrin

An efficient three-component reaction of aromatic aldehyde, 1,3-cyclohexanedione/dimedone, and malononitrile was developed, for the first time, using per-6-amino-β-cyclodextrin, as a supramolecular host for aldehydes and an efficient base catalyst, which produced various substituted 2-amino-4<i>H</i>-benzo­[<i>b</i>]­pyrans in good to excellent yields, under solvent-free conditions. The catalyst can be reused at least three times without any marked change in its catalytic activity. Other remarkable features include a much milder procedure, a shorter reaction time, a wide range of functional group tolerance, and absence of any tedious workup or purification. This procedure also avoids hazardous reagents/solvents and is thus an eco-friendly alternative to the existing methods

Mesoporous Microcapsules through d‑Glucose Promoted Hydrothermal Self-Assembly of Colloidal Silica: Reusable Catalytic Containers for Palladium Catalyzed Hydrogenation Reactions

A facile methodology is reported to fabricate hierarchically ordered silica nanoassembled microcapsules (SiO₂ NACs) with tailored mesopores by combining polymerization of d-glucose with self-assembly of colloidal silica nanoparticles (SiO₂ NPs). This controlled self-assembly of SiO₂ NPs during a hydrothermal process enables the formation of core–shell (organic/inorganic) hybrid microspheres of carbon and SiO₂ NPs. After removal of carbon, spherical hollow SiO₂ NACs are formed having mesopores and their surface area was observed as 248 m²/g. The synthesized mesoporous SiO₂ NACs can be effectively used to encapsulate palladium nanoparticles (Pd NPs) to act as a heterogeneous catalyst in hydrogenation reactions. The position of Pd NPs in SiO₂ NACs (either inside the nanopores or throughout the wall of the capsules) can be dictated by the method of encapsulation which can impart selectivity in hydrogenation of various nitroaromatic compounds, alkyne, and alkenes. The advantages of our catalytic system are greener synthesis of catalyst, that lower Pd content (0.3 mol %) was utilized for the catalytic hydrogenation reaction, heterogeneous nature and reusability

Fabrication of Pd Nanoparticles Embedded C@Fe₃O₄ Core–Shell Hybrid Nanospheres: An Efficient Catalyst for Cyanation in Aryl Halides

Isolated chemical reactors were fabricated by integrating catalytically active sites (Pd) with magnetic functionality (Fe₃O₄) along with carbon while preserving the constituents functional properties to realize the structure–property relationship of Pd by comparing the catalytic activity of spherical Pd NPs with cubical Pd NPs for cyanation in aryl halides using K₄[Fe­(CN)₆] as a green cyanating agent to yield corresponding nitriles. The superior catalytic reactivity of the cubical Pd NPs is attributed to the larger number of {100} surface facets. The TEM images of reused catalyst shows the change in structure from cubical to spherical nanoparticles, attributed to the efficient leaching susceptibility of Pd {100} surface facets. The cubical Pd NPs on carbon@Fe₃O₄ is attractive in view of its high catalytic efficiency, easy synthesis, magnetic separability, environmental friendliness, high stability, gram scale applicability, and reusability

Ultrafine Bimetallic PdCo Alloy Nanoparticles on Hollow Carbon Capsules: An Efficient Heterogeneous Catalyst for Transfer Hydrogenation of Carbonyl Compounds

Monodispersed ultrafine bimetallic palladium–cobalt alloy nanoparticles (Pd_<i>x</i>Co_<i>y</i>) are prepared and immobilized on hollow carbon capsules (HCCs). Studies on the effect of metal composition on the catalytic activity of the Pd_<i>x</i>Co_<i>y</i> reveal that the nanoparticulate alloy with the atomic composition of Pd₃₆Co₆₄ is more active than the Co and Pd monometallic nanoparticles in the transfer hydrogenation of carbonyl compounds. The composition of the catalyst and its alloy formation are extensively characterized, and a variety of ketones and aldehydes are hydrogenated successfully with excellent yield and high turnover number (TON), displaying the ability of the synthesized ultrafine Pd₃₆Co₆₄ bimetallic nanoalloy to attain and retain both high catalytic activity and stability. This catalytic system is heterogeneous, stable and does not require additives for activation. Other advantages include milder reaction conditions (does not use gaseous hydrogen), low metal content (0.17 mol %) for a catalytic transfer hydrogenation reaction, functional group tolerance, environmentally benign nature, and reusability