Metal-free aerobic oxidation of benzazole derivatives

Santos, A. Dos; Kaı̈m, Laurent El; Grimaud, Laurence

doi:10.1039/c3ob27404g

Cited by 23 publications

(12 citation statements)

References 15 publications

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“…Diphenylmethane and its derivatives, which possess electron-donating and electronwithdrawing substituents on the phenylr ings, could be converted into the correspondingb enzophenones,a nd the reactions of substrates with electrondonating substituents proceeded more smoothly than those with electron-withdrawings ubstituents ( Table 3, entries 5-9). Notably,v arious types of structurally diverse N-and S-containing heteroaryl ketones, which are important skeletons for biologically active molecules and potentially useful as synthetic intermediates en route to various pharmaceuticals, [2][3][4][5] could be synthesized effectively from the corresponding heteroalkylarenes (Table 3, entries [10][11][12][13][14]. Phthalan produced the corresponding lactone and carboxylic acid anhydride ( Table 3, entry 15), and 2-phenylacetophenone afforded benzil (Table 3, entry 16).…”

Section: Synthesis and Characterization Of M-mno Xmentioning

confidence: 99%

“…To date, several efficient homogeneous catalytic systems have been reported for aerobic alkylarene oxygenation (Table S1). [6][7][8][9][10][11][12][13][14][15] However,h omogeneous catalysts have severald rawbacks, for example, the use of various additivesa nd the difficulty in catalyst/product separation in exchange for their high catalytic activities. Therefore, the development of efficient heterogeneousc atalysts is desirable, and to date, many research groups have focused on the development of heterogeneous catalysts fora lkylarene oxygenationutilizing O 2 as the oxidant (Tables S2 and S3).…”

Section: Introductionmentioning

confidence: 99%

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Aerobic Oxygenation of Alkylarenes over Ultrafine Transition‐Metal‐Containing Manganese‐Based Oxides

et al. 2018

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The oxygenation of alkylarenes to the corresponding aryl ketones is an important reaction, and the development of efficient heterogeneous catalysts that can utilize O2 as the sole oxidant is highly desired. In this study, we developed an efficient alkylarene oxygenation process catalyzed by ultrafine transition‐metal‐containing Mn‐based oxides with spinel or spinel‐like structures (M‐MnOx, M=Fe, Co, Ni, Cu). These M‐MnOx catalysts were prepared by a low‐temperature reduction method in 2‐propanol‐based solutions using tetra‐n‐butyl ammonium permanganate (TBAMnO4) as the Mn source, and they exhibited high Brunauer–Emmett–Teller surface areas (typically >400 m2 g−1). Using fluorene as the model substrate, the catalytic activities of M‐MnOx and Mn3O4 were compared. The catalytic activities of M‐MnOx were significantly higher than that of Mn3O4, which demonstrates that the incorporation of transition metals in manganese oxide was critical. Among the series of M‐MnOx catalysts examined, Ni‐MnOx exhibited the highest catalytic activity for the oxygenation. In addition, the catalytic activity of Ni‐MnOx was higher than that of a physical mixture of Mn3O4 and NiO. Furthermore, Ni‐MnOx exhibited a broad substrate scope with respect to various types of structurally diverse (hetero)alkylarenes (16 examples). The observed catalysis was truly heterogeneous, and the Ni‐MnOx catalyst was reusable for the oxygenation of fluorene at least three times and its high catalytic performance was preserved, for example, the reaction rate, final product yield, and product selectivity. The present Ni‐MnOx‐catalyzed oxygenation process is possibly initiated by a single‐electron oxidation process, and herein a plausible oxygen‐transfer mechanism is proposed based on several pieces of experimental evidence.

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Section: Synthesis and Characterization Of M-mno Xmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Aerobic Oxygenation of Alkylarenes over Ultrafine Transition‐Metal‐Containing Manganese‐Based Oxides

et al. 2018

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“…The highly investigated Ugi four‐component reactions about arylacetic acids have been widely employed to generate multifunctionalized acyclic adducts for a myriad of intramolecular cyclizations –. Adjusting the structure of aldehydes (R 1 position) or amines (R 2 position)– achieved different one‐pot applications (Scheme ).…”

Section: Electrophilic Acidsmentioning

confidence: 99%

Arylacetic Acids in Organic Synthesis

et al. 2019

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Arylacetic acids are widely used in organic reactions and their recent advances are summarized in six categories according to their triggered pathways: (1) the acid as directing group in ortho-or meta-CÀ H activation; (2) decarboxylation; (3) deprotonation; (4) nucleophilic methylenes; (5) nucleophilic acids; (6) electrophilic acids. Reactions with alkenes, alkynes, aldehydes, amines, water, Grignard reagents, silanes and so forth are discussed. We hope this Minireview will promote future research in this area. Recently, the Zeng group [3g] reported a weakly coordinationassisted alkynylation of arylacetic acids with iridium catalysis under air atmosphere (Eq. 2-2). It was supported the sixmembered ring cycloiridiated 2.5 acted as the key intermediate. The alkynylation of indole, thiophene, pyrrole, and benzo[b] thiophene afforded better yields than phenylacetic acids. The acid moiety could also participated in the intramolecular ortho-CÀ H activation, which was developed by the Shi group to obtain lactonization 2.6 (Eq. 2-3) (Scheme 2). Meta-CÀ H ArylationThe study of Yu group [3e] in 2017 revealed a successful control of meta selectivity 3.1 of arylation from aryl iodides (Eq. 3-1). The use of mono-protected 3-amino-2-hydroxypyridine (as ligand) and 2-carbomethoxynorbornene (NBE-CO 2 Me) were crucial. In the absence of NBE-CO 2 Me, only ortho-arylated product was obtained. This method was still efficient in a gramsale (Scheme 3). Decarboxylation Decarboxylative CouplingAs shown in Scheme 4, the decarboxylation could generate benzyl radicals 4.1. Then, direct couplings of 4.1 with diverse [ + ] These authors contributed equally. Scheme 1. Six categories based on triggered mechanism. 2 3 4 5 6 7 8 . Passerini Three-Component ReactionThe Passerini reaction was the oldest multicomponent reaction (MCR) [37d] in which isocyanides, carboxylic acids and aldehydes were used. It was powerful for the rapid construction of complex molecules. The tactic to expand the scope of Passerini reaction was to use surrogates of the carbonyl partners. As described in Scheme 51, syn-chlorooximes, [37b] diazoketones, [37c] alcohols, [37d,e] azirines [37f] and isatins [37g] could be employed instead of aryl or alkyl aldehydes [37a] (Scheme 51). Besides, in 2018, Zhang and co-workers [37] have firstly reported asymmetric phosphoric acid-catalyzed four-component Ugi reaction, which Scheme 45. BTM-catalyzed cycloaddition. Scheme 46. HBTM-catalyzed cycloaddition. Scheme 47. TFA-catalyzed reaction. Scheme 48. Friedel-Crafts triggered tandem reactions. Scheme 49. C-acylation of 1,3-diones. Scheme 50. C-acylation of 1,3-indandiones.

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“…or PdCl2(CH3CN)2 (10 mol%), CsOPiv (Equation (1)), DMF, 90 °C)). Both methods turned out to be complementary, as in some cases, depending on the substrate, only one of them provided the target 2-aroylbenzothiazole or 2-aroylbenzoimidazole with acceptable yields [131].…”

Section: Palladium Catalystsmentioning

confidence: 99%

“…A base-mediated (Cs 2 CO 3 , Equation (1)) oxidation of 2-benzylbenzothiazole and 2-benzylbenzimidazole derivatives under air atmosphere was presented by Dos Santos et al and the results were compared with those from the oxidation using palladium catalysis (Pd(OAc) 2 (10 mol%) or PdCl 2 (CH 3 CN) 2 (10 mol%), CsOPiv (Equation (1)), DMF, 90 • C)). Both methods turned out to be complementary, as in some cases, depending on the substrate, only one of them provided the target 2-aroylbenzothiazole or 2-aroylbenzoimidazole with acceptable yields [131].…”

Section: Scheme 14 Benzylic C-h Oxidation Of Methylene Compounds By mentioning

confidence: 99%

Recent Advances in Homogeneous Metal-Catalyzed Aerobic C–H Oxidation of Benzylic Compounds

et al. 2018

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Csp 3 -H oxidation of benzylic methylene compounds is an established strategy for the synthesis of aromatic ketones, esters, and amides. The need for more sustainable oxidizers has encouraged researchers to explore the use of molecular oxygen. In particular, homogeneous metal-catalyzed aerobic oxidation of benzylic methylenes has attracted much attention. This account summarizes the development of this oxidative strategy in the last two decades, examining key factors such as reaction yields, substrate:catalyst ratio, substrate scope, selectivity over other oxidation byproducts, and reaction conditions including solvents and temperature. Finally, several mechanistic proposals to explain the observed results will be discussed. relevant parameters such as reaction yields, substrate:catalyst ratio, selectivity towards target carbonyl compounds, reaction media, and other experimental conditions. Considering that metal complexes and combination of metal salts and ligands have been described as catalysts or precatalysts in this field, this review is organized according to the metal core involved in the reaction. Although mechanism for this transformation is far from being completely elucidated, several proposals will be discussed. Catalysts 2018, 8, x FOR PEER REVIEW 2 of 21Following the pioneering works by Ishii [63-66], cobalt(II) salts combined with N-hydroxyphtalimide (NHPI) derivatives have been amply used for the aerobic C-H oxidation of methylene compounds at atmospheric pressure. An in situ-generated phthalimide-N-oxyl radical (PINO) is proposed to play a key catalytic role as hydrogen atom abstracting species in the reaction, and other N-hydroxylated ligand/additives prone to form related radical species have also been evaluated and compared with NHPI. Among other transition metals, cobalt salts have been defined as promoters Catalysts 2018, 8, 640 3 of 21for the formation of PINO. Nolte and coworkers published the use of 0.5 mol% of Co(OAc) 2 ·4H 2 O combined with NHPI (10 mol%) in acetic acid to perform benzylic oxidation of 2-(hetero)arylacetic esters to the corresponding α-ketoesters at relatively low temperatures (40-80 • C). Lower yields (<30%) were obtained from some o-alkoxylated and brominated substrates, as well as from all the heteroaromatic esters. Finally, with regard to the oxidation of ethylbenzene to acetophenone, several N-hydroxy-phthalimides were evaluated as co-catalysts, achieving good conversion rates (except for nitro-substituted NHPIs) and relatively good acetophenone:1-phenylethanol ratios (59-88:2-5) [94].The solvent-free oxidation of several alkylbenzenes to the corresponding ketones using di-n-decyl-di-methyl ammonium bromide (DDAB) and other phase transfer agents was explored by Patil et al. A 0.5 mol% of the latter quaternary ammonium salt was required along with NHPI (3 mol%) and CoCl 2 ·6H 2 O (1 mol%) to perform the oxidation under oxygen gas flow rate of 110 mL/min at 65 • C, although other metal sources (MnCl 2 (H 2 O) 4 and CrCl 3 (H 2 O) 6 ) and ammonium phase transfer catal...

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Metal-free aerobic oxidation of benzazole derivatives

Abstract: 2-Benzyl benzothiazoles and benzimidazoles are easily oxidized under air and basic conditions to give the corresponding ketones in good yields. The use of palladium acetate as a catalyst has little effect and even gives, in some cases, much lower yields.

Cited by 23 publications

References 15 publications

Aerobic Oxygenation of Alkylarenes over Ultrafine Transition‐Metal‐Containing Manganese‐Based Oxides

Aerobic Oxygenation of Alkylarenes over Ultrafine Transition‐Metal‐Containing Manganese‐Based Oxides

Arylacetic Acids in Organic Synthesis

Recent Advances in Homogeneous Metal-Catalyzed Aerobic C–H Oxidation of Benzylic Compounds

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