Supported gold nanoparticle-catalyzed selective reduction of multifunctional, aromatic nitro precursors into amines and synthesis of 3,4-dihydroquinoxalin-2-ones

The synthesis of 3,4-dihydroquinoxalin-2-ones via the selective reduction of aromatic, multifunctional nitro precursors catalyzed by supported gold nanoparticles is reported. The reaction proceeds through the in situ formation of the corresponding amines under heterogeneous transfer hydrogenation of the initial nitro compounds catalyzed by the commercially available Au/TiO2-Et3SiH catalytic system, followed by an intramolecular C-N transamidation upon treatment with silica acting as a mild acid. Under the present conditions, the Au/TiO2-TMDS system was also found to catalyze efficiently the present selective reduction process. Both transfer hydrogenation processes showed very good functional-group tolerance and were successfully applied to access more structurally demanding products bearing other reducible moieties such as chloro, aldehyde or methyl ketone. An easily scalable (up to 1 mmol), low catalyst loading (0.6 mol%) synthetic protocol was realized, providing access to this important scaffold. Under these mild catalytic conditions, the desired products were isolated in good to high yields and with a TON of 130. A library analysis was also performed to demonstrate the usefulness of our synthetic strategy and the physicochemical profile of the derivatives

Supported Gold Nanoparticle-Catalyzed Selective Reduction of Multifunctional, Aromatic Nitro Precursors into Amines and Synthesis of 3,4-Dihydroquinoxalin-2-Ones

The synthesis of 3,4-dihydroquinoxalin-2-ones via the selective reduction of aromatic, multifunctional nitro precursors catalyzed by supported gold nanoparticles is reported. The reaction proceeds through the in situ formation of the corresponding amines under heterogeneous transfer hydrogenation of the initial nitro compounds catalyzed by the commercially available Au/TiO2-Et3SiH catalytic system, followed by an intramolecular C-N transamidation upon treatment with silica acting as a mild acid. Under the present conditions, the Au/TiO2-TMDS system was also found to catalyze efficiently the present selective reduction process. Both transfer hydrogenation processes showed very good functional-group tolerance and were successfully applied to access more structurally demanding products bearing other reducible moieties such as chloro, aldehyde or methyl ketone. An easily scalable (up to 1 mmol), low catalyst loading (0.6 mol%) synthetic protocol was realized, providing access to this important scaffold. Under these mild catalytic conditions, the desired products were isolated in good to high yields and with a TON of 130. A library analysis was also performed to demonstrate the usefulness of our synthetic strategy and the physicochemical profile of the derivatives

Gold(III) Chloride-Mediated Transformation of Furfural to the trans-N,N-4,5-Diaminocyclopent-2-enones in the Presence of Anilines

We investigated the efficient approach of a series of trans-N,N-4,5-substituted-diaminocyclopent-2-enones (trans-DACPs) from furfural and anilines mediated by Gold(III) chloride (HAuCl4). The present protocol required a low amount of the catalysts, 1.5 mol%, open air conditions, the absence of any additives, and short reaction times. The desired trans-DACPs were isolated in good to high yields. The protocol was also applied to secondary amines, leading to the corresponding 4,5-diamino-cyclopent-2-enones in good yields. To the best of our knowledge, this is the first gold-mediated paradigm as an efficient catalyst for the formation of the cyclopentenones core-bearing C-N bonds under mild reaction conditions

Direct and Indirect Chemiluminescence: Reactions, Mechanisms and Challenges

Emission of light by matter can occur through a variety of mechanisms. When it results from an electronically excited state of a species produced by a chemical reaction, it is called chemiluminescence (CL). The phenomenon can take place both in natural and artificial chemical systems and it has been utilized in a variety of applications. In this review, we aim to revisit some of the latest CL applications based on direct and indirect production modes. The characteristics of the chemical reactions and the underpinning CL mechanisms are thoroughly discussed in view of studies from the very recent bibliography. Different methodologies aiming at higher CL efficiencies are summarized and presented in detail, including CL type and scaffolds used in each study. The CL role in the development of efficient therapeutic platforms is also discussed in relation to the Reactive Oxygen Species (ROS) and singlet oxygen (1O2) produced, as final products. Moreover, recent research results from our team are included regarding the behavior of commonly used photosensitizers upon chemical activation under CL conditions. The CL prospects in imaging, biomimetic organic and radical chemistry, and therapeutics are critically presented in respect to the persisting challenges and limitations of the existing strategies to date

Selective Synthesis of Benzimidazoles from o-Phenylenediamine and Aldehydes Promoted by Supported Gold Nanoparticles

We investigated the catalytic efficacy of supported gold nanoparticles (AuNPs) towards the selective reaction between o-phenylenediamine and aldehydes that yields 2-substituted benzimidazoles. Among several supported gold nanoparticle platforms, the Au/TiO2 provides a series of 2-aryl and 2-alkyl substituted benzimidazoles at ambient conditions, in the absence of additives and in high yields, using the mixture CHCl3:MeOH in ratio 3:1 as the reaction solvent. Among the AuNPs catalysts used herein, the Au/TiO2 containing small-size nanoparticles is found to be the most active towards the present catalytic methodology. The Au/TiO2 can be recovered and reused at least five times without a significant loss of its catalytic efficacy. The present catalytic synthetic protocol applies to a broad substrate scope and represents an efficient method for the formation of a C–N bond under mild reaction conditions. Notably, this catalytic methodology provides the regio-isomer of the anthelmintic drug, Thiabendazole, in a lab-scale showing its applicability in the efficient synthesis of such N-heterocyclic molecules at industrial levels

Both bronchial and alveolar exhaled nitric oxide are reduced with extrafine beclomethasone dipropionate in asthma.

Exhaled nitric oxide (NO) is a noninvasive marker of airway inflammation. Beclomethasone dipropionate (BDP) is the only inhaled corticosteroid (ICS) available as both extrafine and nonextrafine hydrofluoroalkane (HFA) pressurized metered-dose inhaler (pMDI) formulation. The present study was designed to evaluate whether the different patterns of lung deposition of two HFA BDP formulations are associated with a different effect on bronchial and alveolar NO. This was a prospective double-blind, randomized, controlled, crossover study. After a 2-week placebo run-in period without ICSs, asthmatic patients were randomized to extrafine BDP, 100 μg, b.i.d. or nonextrafine BDP, 250 μg, b.i.d. for two 2-week periods separated by a 2-week washout period. Fourteen patients (5 men) with a mean age 37 years and mean baseline forced expiratory volume in 1 second (FEV1) of 83% of predicted were analyzed. Exhaled bronchial NO was significantly (p < 0.001) reduced in both treatment groups when compared with the last week of run-in period, whereas alveolar NO was significantly (p < 0.001) reduced only with extrafine BDP. Moreover, extrafine BDP was superior to nonextrafine BDP in both parameters (p < 0.05). Extrafine but not nonextrafine BDP HFA formulation lowers both bronchial and alveolar exhaled NO in asthmatic patients. ICS distribution throughout the whole bronchial tree could be important in patients who do not gain optimal control of inflammation with conventional nonextrafine ICS

Mo2C as Pre-Catalyst for the C-H Allylic Oxygenation of Alkenes and Terpenoids in the Presence of H2O2

In this study, commercially available molybdenum carbide (Mo2C) was used, in the presence of H2O2, as an efficient pre-catalyst for the selective C-H allylic oxygenation of several unsaturated molecules into the corresponding allylic alcohols. Under these basic conditions, an air-stable, molybdenum-based polyoxometalate cluster (Mo-POM) was formed in situ, leading to the generation of singlet oxygen (1O2), which is responsible for the oxygenation reactions. X-ray diffraction, SEM/EDX and HRMS analyses support the formation mainly of the Mo6O192&minus; cluster. Following the proposed procedure, a series of cycloalkenes, styrenes, terpenoids and methyl oleate were successfully transformed into hydroperoxides. After subsequent reduction, the corresponding allylic alcohols were produced with good yields and in lab-scale quantities. A mechanistic study excluded a hydrogen atom transfer pathway and supported the twix-selective oxygenation of cycloalkenes on the more sterically hindered side via the 1O2 generation

Mo₂C as Pre-Catalyst for the C-H Allylic Oxygenation of Alkenes and Terpenoids in the Presence of H₂O₂

In this study, commercially available molybdenum carbide (Mo2C) was used, in the presence of H2O2, as an efficient pre-catalyst for the selective C-H allylic oxygenation of several unsaturated molecules into the corresponding allylic alcohols. Under these basic conditions, an air-stable, molybdenum-based polyoxometalate cluster (Mo-POM) was formed in situ, leading to the generation of singlet oxygen (1O2), which is responsible for the oxygenation reactions. X-ray diffraction, SEM/EDX and HRMS analyses support the formation mainly of the Mo6O192− cluster. Following the proposed procedure, a series of cycloalkenes, styrenes, terpenoids and methyl oleate were successfully transformed into hydroperoxides. After subsequent reduction, the corresponding allylic alcohols were produced with good yields and in lab-scale quantities. A mechanistic study excluded a hydrogen atom transfer pathway and supported the twix-selective oxygenation of cycloalkenes on the more sterically hindered side via the 1O2 generation