Regioselective dehydrogenation of 3,4-dihydropyrimidin-2(1H)-ones mediated by ceric ammonium nitrate

Ceric ammonium nitrate (CAN) has been explored for the regioselective oxidation of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs). Interestingly, we obtained ethyl 2,4-dioxo-6-phenyl-tetrahydropyrimidin-5-carboxylates as the major products during the oxidation of DHPMs by CAN/AcOH at 80 °C. The reaction afforded a mixture of products while employing CAN in organic solvents without additives. However, the regioselective dehydrogenated product, ethyl 6-methyl-4-aryl(alkyl)-pyrimidin-2(1H)-one-5-carboxylate was obtained by performing the reaction with NaHCO₃. The single crystal X-ray crystallography of ethyl 6-methyl-4-(2-phenyl)-pyrimidin-2(1H)-one-5-carboxylate revealed that the oxidized product existed in amidic form rather than aromatized enol form of pyrimidines. The efficiency of the present protocol enabled the synthesis of structurally diverse pyrimidines in moderate to good yields under milder reaction conditions.     

Probing the effect of nitrate anion in CAN: An additional opportunity to reduce the catalyst loading for aerobic oxidations

Catalyzed by cerium ammonium nitrate (CAN), the oxidative cracking reaction of alkenes occurred to produce carbonyls in good yields under mild conditions. The reaction employed molecular oxygen (O₂) as the safe and clean oxidant. The catalyst dosage was reduced to as low as 0.5 mol%, while no additive was required. Thus, it may afford a generally green synthetic approach for introducing oxygen into organic molecules as well as the biomass degradation and the resource recycling from the C=C bond-containing waste polymers. X-ray photoelectron spectroscopy (XPS) analysis and control experiments demonstrated that the process proceeded via a single electron transfer (SET) reaction-initiated free radical reaction mechanism. In the process, both Ce and NO₃⁻ acted as the oxygen carrier to promote the oxidation reaction. The application of the abundantly existed nitrate in CAN was found to be the key for reducing the catalyst loading.     

Reactivity of polyhydroxyalkyl-heterocycles towards Lewis acids

We report the reactivity of different polyhydroxyalkyl-heterocycles towards ceric ammonium nitrate (CAN) and ferric chloride. The behaviour of 2-methyl-5-(tetritol-1-yl)-pyrroles and -furans is different towards CAN oxidation. Pyrroles afford 2,5-diformylheterocycles, while furans give access to 1,4-dicarbonyl compounds containing three stereogenic centres. Ferric chloride promotes an intramolecular C-arylation reaction on O-benzylated-polyhydroxyalkyl furans, yielding an isochroman moiety, which is the basic skeleton of a variety of natural products.     

Sodium N-chloro-p-nitrobenzenesulfonamide (chloramine-N) as a new redox titrant: I. The status of chloramine-N as a titrimetric reagent

The status of sodium N-chloro-p-nitrobenzenesulfonamide (chloramine-N) as a new redox titrant is examined. Analytical applications of CAN as a potential titrimetric reagent in the direct determination of diverse reducing agents such as glutathione, thioglycolic acid, thiourea, ascorbic acid, methionine, sulfite, and arsenite have been described. CAN has been synthesized and its structure elucidated from the spectral data and elemental analyses. The ultraviolet and infrared spectra and Fourier transform ¹H and ¹³C nuclear magnetic resonance spectral data have been presented.     

Cerium ammonium nitrate (CAN) for mild and efficient reagent to remove hydroxyethyl units from 2-hydroxyethyl ethers and 2-hydroxyethyl amines

Cerium ammonium nitrate (CAN) removed hydroxyethyl units from 2-hydroxyethyl ethers and 2-hydroxyethyl amines to produce alcohols and amines in good yields. Especially, removal of the 2-hydroxyethyl ethers from C₂-symmetric diols, chiral 2,3-butanediol and chiral hydrobenzoin, was very useful for asymmetric syntheses using C₂-symmetric diols. The reactions using dual abilities of CAN, i.e., the ability for removal of the 2-hydroxyethyl unit and the ability for acetal hydrolysis by a single electron transfer, were also achieved successfully. The reaction conditions were very mild and efficient, and many functional groups, which can be affected under normal conditions, were unaffected during the reaction.     

Influence of alloying platinum for the hydrogenation of p-chloronitrobenzene over PtM/Al2O3 catalysts with MSn,Pb, Ge,Al, Zn

Hydrogenation of p-chloronitrobenzene (CNB) has been studied, in methanol suspension, at 303 K and atmospheric pressure, over a series of Pt/Al₂O₃ and PtM/Al₂O₃ catalysts (MSn, Pb, Ge, Al, Zn). The bimetallic catalysts were prepared by the so-called controlled surface reaction method by reacting organometallic compounds on the well-dispersed Pt/Al₂O₃ parent sample. The kinetics obeys a modified Langmuir-Hinshelwood model with competitive adsorption between CNB and hydrogen. The competition of adsorption no longer holds at high CNB concentration: on the Pt surface saturated by CNB, there are still Pt sites available for the chemisorption of the smaller hydrogen molecule. A rate law is then proposed which allows both adsorption and rate constants to be determined. Upon addition of the second metal M, the specific activity per Pt surface atom goes through a maximum value around a chemical composition M/Pt≌0.1–0.2. It is suggested that an electron-deficient species of the second metal promotes the reaction rate by activating the nitrogenoxygen bond; ionic tin species are better promoters for this purpose. At high CNB conversion (> 98%) the yield of the desired product, p-chloroaniline (CAN), increases from 82% on pure Pt/Al₂O₃ to 97.5% on PtSn/Al₂O₃ (Sn/Pt = 0.36). The improvement of selectivity to CAN is not due to a decrease in CAN dehalogenation rate, which is not affected by alloying. Actually, the promoting effect of the second metal decreases the relative strength of adsorption between CAN and CNB up to a factor of 10: CAN is then easily removed from the surface by CNB, thus preventing hydrodechlorination.     

The synthesis of heterocyclic derivatives from pyran-2-ones and hydrazine hydrate. Ammonium cerium(IV) nitrate as an efficient oxidant in pyridazine chemistry

A novel reaction of 3-amino-2H-pyran-2-ones and their fused derivatives with hydrazine hydrate leading to the corresponding pyridazine derivatives is reported. Further oxidation with ammonium cerium(IV) nitrate (CAN, from Cerium(IV) Ammonium Nitrate) yields a collection of pyridazine-3-carboxylates.     

Cerium (IV) ammonium nitrate-mediated reactions: Simple route to benzimidazole derivatives

The reaction of o-phenylenediamine with aromatic aldehydes in MeOH at room temperature catalyzed by cerium (IV) ammonium nitrate (CAN) afforded either 2-aryl-1-arylmethyl-1H-benz-imidazoles and/or 2-aryl-substituted benzimidazoles.     

(NH4)2Ce(NO3)6 as an inexpensive,eco-friendly,efficient catalyst for the synthesis of 5-substituted 1-H tetrazoles from nitriles

Ceric ammonium nitrate (CAN) is found to be a suitable, inexpensive, and effective non-toxic catalyst for a smooth (3+2) cycloaddition of organic nitriles with NaN₃ to afford 5-substituted 1H-tetrazoles in excellent yields. Shorter reaction times, easy work-up, and substantial and pure product formation are the key advantages of the present method.     

Secondary Effects of Hypochlorite Treatment on the Emerging Pollutant Candesartan: The Formation of Degradation Byproducts and Their Toxicological Profiles

In recent years, many studies have reported the frequent detection of antihypertensive agents such as sartans (olmesartan, valsartan, irbesartan and candesartan) in the influents and effluents of wastewater treatment plants (WWTPs) and in the superficial waters of rivers and lakes in both Europe and North America. In this paper, the degradation pathway for candesartan (CAN) was investigated by simulating the chlorination process that is normally used to reduce microbial contamination in a WWTP. Twelve isolated degradation byproducts (DPs), four of which were isolated for the first time, were separated on a C-18 column by employing a gradient HPLC method, and their structures were identified by combining nuclear magnetic resonance and mass spectrometry and comparing the results with commercial standards. On the basis of these results, a mechanism of formation starting from the parent drug is proposed. The ecotoxicity of CAN and its DPs was studied by conducting a battery of ecotoxicity tests; bioassays were performed using Aliivibrio fischeri (bacterium), Daphnia magna (planktonic crustacean) and Raphidocelis subcapitata (alga). The ecotoxicity results shed new light on the increased toxicity of DPs compared with the parent compound.     

In Situ Synthesis of Manganese Oxide as an Oxygen-Evolving Catalyst: A New Strategy

All studies on oxygen-evolution reaction by Mn oxides in the presence of cerium(IV) ammonium nitrate (CAN) have been so far carried out by synthesizing Mn oxides in the first step. And then, followed by the investigation of the Mn oxides in the presence of oxidants for oxygen-evolution reaction (OER). This paper presents a case study of a new and promising strategy for in situ catalyst synthesis by the adding Mn^II to either CAN or KMnO₄/CAN solution, resulting in the formation of Mn-based catalysts for OER. The catalysts were characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Both compounds contained nano-sized particles that catalyzed OER in the presence of CAN. The turnover frequencies for both catalysts were 0.02 (mmol /mol_Mn⋅s).     

Cerium(IV)-mediated C-C bond formations in carbohydrate chemistry

We provide a comprehensive study on the addition of radicals to unsaturated carbohydrates in the presence of cerium(IV) ammonium nitrate (CAN). The method is applicable to hexoses, pentoses, and disaccharides, tolerates different protecting groups, and is characterized by mild reaction conditions. Best substrates are malonates and glycals, which afford 2-C-branched carbohydrates in high yields and stereoselectivities. For the first time, the anomeric radicals were trapped with nucleophiles after oxidation and thus the 1- and 2-position of glucose were functionalized in one step. Nitro compounds are suitable CH acidic radical precursors as well, offering an easy access to C-analogs of glycosamines in moderate to good yields. Finally, selective reductions demonstrate the synthetic potential of cerium(IV)-mediated radical reactions in carbohydrate chemistry.     

Reactions promoted by [hydroxy(tosyloxy)iodo]benzene in pyrazino[1,2-b]isoquinolines

The hypervalent iodine reagent PhI(OH)OTs (HTIB) promoted oxidative demethylation of 1,4-hydroquinone methyl ethers to give quinones in a quantitative conversion. The efficacy of this reaction, that has been applied to simple arene compounds and to heterocyclic systems, such as 2-isopropoxycarbonyl-7,10-dimethoxy-pyrazino[1,2-b]isoquinoline-4-ones and 1,4-diones to get the corresponding 7,10-quinones (compounds 6-8), is similar to those promoted by CAN and does not require the presence of water. Instead of oxidative demethylation, HTIB promoted in 1-methoxy-pyrazino[1,2-b]isoquinoline-4-ones complex multi-step processes to give compounds 9 or 10.     

A versatile approach for the asymmetric synthesis of 3-alkyl-2,3-dihydro-1H-isoindolin-1-ones

Based on the use of (R)-p-benzyloxyphenylglycinol (10) as a new oxidatively cleavable chiral auxiliary, a flexible approach to (R)-3-alkyl-2,3-dihydro-1H-isoindolin-1-ones via a diastereoselective reductive-alkylation is developed. The oxidative cleavage of the chiral auxiliary by CAN under mild conditions ensured the access to (R)-3-alkyl-2,3-dihydro-1H-isoindolin-1-ones with ee at least 92%.     

Eco-efficient one-pot tandem synthesis of 1-aryl-1H-tetrazol-5-amine by CAN via in situ generated 1-phenylthiourea and heterocumulene

A simple, cost-effective, environmentally benign, and efficient one-pot tandem approach to the synthesis of pharmaceutically important 1-aryl-1H-tetrazole-5-amines 3a-k and 4a-k has been described. The reaction utilized 1-phenyl thiourea, which was generated in situ from aqueous ammonia and isocyanates 1a-k, for the formation of heterocumenes using sodium azide, triethylamine, and ceric ammonium nitrate (CAN) to obtain various aryl-substituted 1H-tetrazole-5-amines (3a-k) in good to excellent yields.     

A mild and efficient CAN mediated oxidation of Morita-Baylis-Hillman adducts of 5-methyl-N-alkylisatin to 5-formyl-N-alkylisatin

A simple, mild and efficient CAN mediated oxidation of Morita-Baylis-Hillman adducts of 5-methyl-N-alkylisatins 1a-13a to 5-formyl-N-alkylisatins 1b-13b under ambient reaction conditions is reported. Simple and isomerized 5-methyl-N-alkylisatin derivatives 1-4 have also been tested and failed to provide the corresponding formylated products. A plausible reaction mechanism has been proposed.     

Oxidative polymerization of N-substituted carbazoles

Poly(N-vinylcarbazole), poly(N-carbazole) and poly(N-ethylcarbazole) powders were chemically synthesized by the reaction of ceric ammonium nitrate (CAN) with N-vinylcarbazole carbazole and N-ethylcarbazole in acetonitrile. Products were characterized by elemental analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and viscosity, X-ray fluorescence and four-probe conductivity measurement. It is found that when a suitable concentration of CAN is used in the polymerization process, the conductivity of chemically synthesized polymers can be improved further by controlling the CAN addition. © 1997 John Wiley & Sons, Ltd.     

Brønsted acidity of ceric ammonium nitrate in anhydrous DMF. The role of salt and solvent in sucrose cleavage

The generation of an unexpected Brønsted acidity in anhydrous DMF at 50 °C was evidenced by NMR measurements during the investigation on the course of sucrose cleavage by ceric ammonium nitrate (CAN). The formation of a nitrooxy derivative of DMF by reaction with CAN is responsible for this acidity. The reactivity of CAN at 50 °C with several solvents was evaluated by voltammetric and potentiometric measurements. The possible release of protons from these reactions, particularly when aqueous solvent mixtures are used, should always be taken into account in the mechanistic interpretation of CAN synthetic applications.     

Cerium (IV) ammonium nitrate catalyzed photochemical autoxidation of alkylbenzenes

The autoxidation of alkylbenzenes can be promoted photochemically in the presence of catalytic amounts of cerim (IV) ammonium nitrate (CAN) under very mild conditions, the efficiency of the process being significantly increased by added acids. It is suggested that the reaction is promoted by NO₃, radicals formed in the light induced decomposition of CAN and that Ce(III) may be reoxidized to Ce(IV) by benzylperoxy radicals.     

Optimization of Preparation Process for Allylamine-bacterial Cellulose via Graft Copolymerization by Response Surface Methodology

In order to improve the efficiency of new adsorbent, grafting-allylamine bacterial cellulose（al-BC）, response surface methodology（RSM） was used for the optimization of preparation process. Three factors affecting the yield of grafting reaction are the amount of allylamine, the concentration of ceric ammonium nitrate（CAN） and the concentration of nitric acid. Based on the regression coefficient analysis in the Box-Behnken design, a relationship between the preparation variable and grafting yield was obtained. Square error analysis on main factors, and multi-variable interactions were employed for studying grafting yield. The results show that at the conditions of CAN of 23.00 mmol/L CAN, 0.17 mol/L nitric acid, adding an amount of grafting-allylamine bacterial cellulose of 26.49 mL/L made grafting rate reach maximum of 24.25% at 40℃ after the reaction for 4 h. The experimental results are in good agreement with the calculation values via proposed regression equation, indicating that the equation could be used to nredict and optimizate the preparation of grafting al-BC.