Base and Catalyst-Free Synthesis of Nitrobenzodiazepines via a Cascade NNitroallylation- Intramolecular Aza-Michael Addition involving o-Phenylenediamines and Nitroallylic Acetates

Published ArticleA [4+3] annulation of o-phenylenediamines with primary nitroallylic acetates affords nitrobenzodiazepines (NBDZs) in good to excellent yield. The reaction which proceeds in MeOH at room temperature in the absence of any base or catalyst involves a cascade SN2 Nnitroallylation- intramolecular aza-Michael addition sequence. In the case of mono-N-arylated ophenylenediamines and o-aminobenzamides, the reaction stops at the SN2 stage affording nitroallylic amines. On the other hand, reaction of o-aminobenzamides with secondary nitroallylic acetates delivers SN2’ products. Formation of stable SN2 and SN2’ products provides insights into the reactivity of primary and secondary nitroallylic acetates and also the mechanism of formation of nitrobenzodiazepines

Selective conversion of nitroarenes using a carbon nanotube-ruthenium nanohybrid

International audienceRuthenium nanoparticles were assembled on carbon nanotubes and the resulting nanohybrid was used in the hydrazine-mediated catalytic hydrogenation of various nitroarenes, at room temperature. Depending on the solvent, a selective transformation occurred, giving either access to the corresponding aniline or hydroxylamine derivative

Room temperature Suzuki coupling of aryl iodides, bromides, and chlorides using a heterogeneous carbon nanotube-palladium nanohybrid catalyst

International audiencePalladium nanoparticles were immobilized on multi-walled carbon nanotubes by a layer-by-layer approach, resulting in a well-defined assembly. The nanohybrid was found effective in promoting Suzuki cross couplings of various halogenated aromatics, including chlorinated ones, with arylboronic acids under sustainable conditions. The heterogeneous catalyst could also easily be recovered from the reaction mixture and reused with no loss of activity over several cycles

The Electrochemical Behaviour of Novel Multifunctional a-Hydroxymethylated Nitroalkenes at Glassy Carbon and Wax Impregnated Carbon Paste Electrodes

The electrochemical behaviour of novel multifunctional a-hydroxymethylated nitroalkenes was studied with respect to oxidation of –OH moiety and reduction of nitro group using the cyclic voltammetric technique at glassy carbon and wax impregnated carbon paste electrodes with sulphuric acid as the supporting electrolyte. The –OH moiety attached to the nitroalkene side chain was found to undergo irreversible four electrons electrochemical oxidation to form an acid at the glassy carbon electrode but no oxidation was observed at the wax impregnated carbon paste electrode. Oxidation in sulphuric acid medium becomes easier with increasing the sulphuric acid concentration. This unusual behaviour is attributed to the formation of a sixmembered cyclic structure at lower concentrations of sulphuric acid due to intramolecular hydrogen bonding. Going to the lower potential range, reduction of nitro group was observed in sulphuric acid medium both at the glassy carbon and wax impregnated carbon paste electrodes. A comparative study indicated easier reduction at the glassy carbon electrode. Non hydroxymethylated beta nitroalkenes undergo reduction at a lower negative potential compared to the corresponding a-hydroxymethylated nitroalkenes

Mild and selective catalytic oxidation of organic substrates by a carbon nanotube-rhodium nanohybrid

International audienceA heterogeneous catalyst was assembled by stabilization of rhodium nanoparticles on carbon nanotubes. The nanohybrid was used for the catalytic aerobic oxidation of diverse substrates such as hydroquinones, hydroxylamines, silanes, hydrazines and thiols, at room temperature. The system proved very efficient on the investigated substrates and demonstrated high selectivity. The selective oxidation of organic compounds under mild conditions is of practical importance in synthetic chemistry. In addition to classical stoichiometric processes, catalytic systems have been devised to perform oxidation reactions. 1 Further improvements in terms of sustainability were also achieved by supporting the catalysts, thus allowing their reclaim and reuse. 2 Among the various catalyst supports, nanostructured carbon allotropes, in particular carbon nanotubes (CNTs), have emerged as highly promising platforms that provide unique advantages such as chemical, thermal, and mechanical stability in liquid media, inertness, high specific surface area, and chemically tunable topography. 3 We previously reported supramolecular assemblies of metallic nanoparticles (e.g. Au, Pd, Ru) on carbon nanotubes. These assemblies afforded metal-coated CNTs that were subsequently used in the heterogeneous catal-ysis of various organic transformations. 4 In the course of our investigations we demonstrated that CNTs acted as synergistic support capable of enhancing the performances of the catalytic metal. With these critical features in mind, we sought to expand the scope of our nanohybrid systems by developing a catalyst that would promote a broad scope of oxidation reactions under mild and sustainable conditions

Direct and co-catalytic oxidative aromatization of 1,4-dihydropyridines and related substrates using gold nanoparticles supported on carbon nanotubes

International audienceA heterogeneous catalyst was assembled by stabilization of gold nanoparticles on carbon nanotubes. The resulting nanohybrid was used in the catalytic aerobic oxidation of 1,4-dihydropyridines. The system proved very efficient on the investigated substrates either directly or in the presence of a quinone co-catalyst. Pyridines have found applications in various domains such as in the synthesis of drugs, 1 herbicides, 2 or insecticides. 3 In addition, the pyridine scaffold plays a central role in living systems since nicotinamide adenine dinucleotide (NAD + / NADH) and nicotinamide adenine dinucleotide phosphate (NADP + /NADPH) are key pyridine-incorporating co-factors involved in oxido-reduction processes. 4 Among the various methods developed for the synthesis of pyridine derivatives, 5 the oxidation of Hantzsch 1,4-dihydropyridines is likely one of the most straightforward approaches. The Hantzsch pyridine synthesis is a multi-component process which involves an aldehyde, two equivalents of a β-keto ester, and a nitrogen atom source. The initial condensation affords a dihydro-pyridine intermediate which can be oxidized, in a second step, into the corresponding pyridine. This reaction was reported for the first time in 1881 by Arthur Hantzsch. 6 Numerous reagents have been reported to promote the second step-oxidative aromatization reaction and include, for example , copper bromide, 7 ferric chloride, 8 palladium on carbon, 9 manganese dioxide, 10 and tert-butylhydroperoxide. 11 However, the oxidation of dihydropyridines is not always easy when substrates bear sensitive functional groups and there is still the quest for mild and general protocols. Also, some of the reported procedures lead to the formation of by-products which can be difficult to remove from the reaction mixture. Therefore, the development of milder, sustainable, and more effective methods for the oxidative aromatization of 1,4-dihydropyridines is sound. In the present article, we report the assembly and use of a recyclable CNT-supported gold catalyst for the selective and mild aerobic oxidation of 1,4-dihydropyridines (DHPs) and related substrates (Fig. 1). The CNT-gold catalyst was assembled using a layer-by-layer approach according to a previously reported procedure Fig. 1 Overview of the catalytic assembly and catalyzed oxidation process studied in the present work

Regio- and Diastereoselective Synthesis of Dihydropyridopyrimidines via Cascade Reactions of 2‑Aminopyridines with Morita–Baylis–Hillman Bromides of Nitroalkenes

The Morita–Baylis–Hillman (MBH) bromides of nitroalkenes have been employed as bielectrophiles for the first time. The 1,3-bielectrophilic reactivity of the MBH bromides has been demonstrated in the synthesis of 3,4-dihydro-2<i>H</i>-pyrido­[1,2-<i>a</i>]­pyrimidines. The reaction of MBH bromides with 2-aminopyridines takes place in the absence of any reagent in a cascade S_N2′-6-endo-trig fashion and is completely regioselective and highly stereoselective. The products, in their hydrobromide salt form, could be conveniently isolated and purified by crystallization. The high stereoselectivity has been rationalized in terms of the greater stability of the transition state in which the Ar and NO₂ groups are anti to each other

Enantioselective Synthesis of Quaternary α-Aminophosphonates via Conjugate Addition of α-Nitrophosphonates to Enones

Enantioselective Michael addition of <b>α</b>-nitrophosphonates to enones for the synthesis of <b>α</b>-aminophosphonates is reported for the first time. The reaction proceeds in good to high yields and moderate to high selectivity in the presence of a new quinine thiourea catalyst. The quaternary nitrophosphonates were conveniently transformed to cyclic quaternary <b>α</b>-aminophosphonates via in situ reduction–intramolecular cyclization or Baeyer–Villiger oxidation followed by in situ reduction–intramolecular cyclization

Regio- and Diastereoselective Synthesis of Dihydropyridopyrimidines via Cascade Reactions of 2‑Aminopyridines with Morita–Baylis–Hillman Bromides of Nitroalkenes

The Morita–Baylis–Hillman (MBH) bromides of nitroalkenes have been employed as bielectrophiles for the first time. The 1,3-bielectrophilic reactivity of the MBH bromides has been demonstrated in the synthesis of 3,4-dihydro-2<i>H</i>-pyrido­[1,2-<i>a</i>]­pyrimidines. The reaction of MBH bromides with 2-aminopyridines takes place in the absence of any reagent in a cascade S_N2′-6-endo-trig fashion and is completely regioselective and highly stereoselective. The products, in their hydrobromide salt form, could be conveniently isolated and purified by crystallization. The high stereoselectivity has been rationalized in terms of the greater stability of the transition state in which the Ar and NO₂ groups are anti to each other

Quinine-Derived Thiourea and Squaramide Catalyzed Conjugate Addition of α‑Nitrophosphonates to Enones: Asymmetric Synthesis of Quaternary α‑Aminophosphonates

Conjugate addition of α-nitrophosphonates to enones was carried out in the presence of two sets of organocatalysts, viz. a quinine-thiourea and a quinine-squaramide. The quinine-thiourea provided the products possessing an α-quaternary chiral center in high enantioselectivities only in the case of electron rich enones. On the other hand, the quinine-squaramide was more efficient in that a wide variety of electron rich and electron poor enones underwent Michael addition of nitrophosphonates to afford the quaternary α-nitrophosphonates in excellent yields and enantioselectivities. The hydrogen bonding donor ability of the bifunctional catalyst, as shown in the proposed transition states, appears primarily responsible for the observed selectivity. However, a favorable π-stacking between the aryl groups of thiourea/squaramide and aryl vinyl ketone also appeared favorable. The reaction was amenable to scale up, and the enantioenriched quaternary α-nitrophosphonates could be easily transformed to synthetically and biologically useful quaternary α-aminophosphonates and other multifunctional molecules