Oxidative Aromatization Research Articles

Correction: Application of the Cu(i)/TEMPO/O2 catalytic system for aerobic oxidative dehydrogenative aromatization of pyrrolidines

Correction for ‘Application of the Cu(i)/TEMPO/O2 catalytic system for aerobic oxidative dehydrogenative aromatization of pyrrolidines’ by Zheng Luo et al., Green Chem., 2019, 21, 4609–4613.

Bidirectional enantioselective synthesis of bis-benzofuran atropisomeric oligoarenes featuring two distal C–C stereogenic axes

We report the bidirectional enantioselective synthesis of bis-benzofuran atropisomeric oligoarenes featuring two distal C-C stereogenic axes obtained by a two-fold central-to-axial chirality conversion upon oxidative aromatization. The key enantioenriched centrally chiral bis-dihydrobenzofuran precursors were synthesized via a bidirectional diastereo- and enantio-selective organocatalyzed domino reaction between simple achiral and easily accessible dihydroxylated aromatics and chloronitroalkenes. Moreover, the stereodivergent nature of the methodology was established by synthesizing both diastereomers of a non-symmetrically functionalized bis-axially chiral oligoarene.

One-Pot Synthesis of N-Alkyl Indole from Indoline-2-carboxylic Acids and Alkyl Halides by 2,3-Dicyano-5,6-dichlorobenzoquinone (DDQ) Mediated Oxidative Decaboylative Aromatization

One-Pot Synthesis of <i>N</i>-Alkyl Indole from Indoline-2-carboxylic Acids and Alkyl Halides by 2,3-Dicyano-5,6-dichlorobenzoquinone (DDQ) Mediated Oxidative Decaboylative Aromatization

Facile Synthesis of Polysubstituted Indolizines via One-Pot Reaction of 1-Acetylaryl 2-Formylpyrroles and Enals.

An efficient method for the synthesis of polysubstituted indolizines has been developed based on formal [4+2] annulation of 1-acetylaryl 2-formylpyrroles with enals, followed by oxidative aromatization. Pyridine-type six-membered rings were constructed in this transformation. This transition metal-free reaction features mild reaction conditions, a broad substrate scope, and excellent functional group tolerance. Notably, the formyl group is well tolerated under reaction conditions.

Synthesis and X‐ray single crystal structure of first aromatic ortho‐di‐tert‐butyl azolo[1,2,4]triazine

AbstractOxidation of 3,4‐di‐tert‐butyl‐8‐methyl‐1,4‐dihydropyrazolo[5,1‐c][1,2,4]triazine with NBS/K2CO3 furnished 3,4‐di‐tert‐butyl‐8‐methylpyrazolo[5,1‐c][1,2,4]triazine, a mildly strained heteroaromatic compound. X‐Ray single crystal diffraction analysis indicated that the conjugated 1,2,4‐triazine ring adopts a twist‐boat configuration, while the two t‐Bu substituents are located on the opposite sides of the azole plane. The related 3‐tert‐butyl‐4‐(o‐C‐carboranyl)‐8‐methyl‐1,4‐dihydropyrazolo[5,1‐c][1,2,4]triazine was also synthesized, however, its oxidative aromatization was unsuccessful.

Rapid and Efficient Construction of Indolizino[3,4,5‐ab]isoindole Skeletons by a Rhodium‐Catalyzed Tandem Reaction

AbstractA facile rhodium‐catalyzed tandem reaction of two molecules of acrylates with two molecules of 2‐phenylpyridines involving sequential C−H activation, Michael addition, [12+2] cycloaddition and oxidative aromatization has been described. A series of indolizino[3,4,5‐ab]isoindole compounds were efficiently afforded in good yields by the formation of two C−C bonds, two C=C bonds and one C−N bond.

1 H -1,2,4-TRIAZOLO-5-DIAZONIUM SALTS IN THE SYNTHESIS OF NOVEL [1,2,4]TRIAZOLO[1,5- c ][1,2,4]BENZOTRIAZIN-6-OLS

Condensation of 1H-1,2,4-triazolo-5-diazonium salts with 1,3-cyclohexanedione, accompanied by cascade processes of cyclization and oxidative aromatization, brought about the synthesis of novel derivatives of [1,2,4]triazolo[5,1-c][1,2,4]benzotriazin-6-ols.

1H-1,2,4-Triazolo-5-diazonium salts in the synthesis of novel [1,2,4]triazolo[1,5-c][1,2,4]benzotriazin-6-ols

Condensation of 1H-1,2,4-triazolo-5-diazonium salts with 1,3-cyclohexanedione, accompanied by cascade processes of cyclization and oxidative aromatization, brought about the synthesis of novel derivatives of [1,2,4]triazolo[5,1-c][1,2,4]benzotriazin-6-ols.

Inter- and Intramolecular Alkyne–Carbonyl Metathesis/1,6-Addition/Oxidative Aromatization Tandem Reactions between 1,6-Diynes and Aldehydes

We report an efficient synthetic route to 9-arylfluorenes and biaryl compounds from 1,6-diynes and aldehydes via inter- and intramolecular alkyne-carbonyl metathesis/1,6-addition/oxidative aromatization reactions. These tandem reactions are initiated by a BF3·Et2O-promoted tandem inter- and intramolecular alkyne-carbonyl metathesis of 1,6-diynes with carbonyl compounds followed by an In(OTf)3-catalyzed 1,6-addition/oxidative aromatization with iodobenzene diacetate.

Synthesis of Quaternary Carbon-Centered Benzoindolizidinones via Novel Photoredox-Catalyzed Alkene Aminoarylation: Facile Access to Tylophorine and Analogues

Photoredox-catalyzed aminoarylation and thioamination of unactivated alkenes have been developed, providing novel synthetic routes to access synthetically challenging quaternary carbon-centered ben...

A Serendipitous Synthesis: SiO2‐HNO3 Mediated Oxidative Aromatization and Regioselective Nitration of 1,3,5‐Trisubstituted‐4,5‐Dihydro‐1H‐Pyrazoles

AbstractResearch often leads to unprecedented results that open the gates for new methodologies. We report herein the oxidative aromatization and serendipitous regioselective nitration of 1,3,5‐trisubstituted‐4,5‐dihydro‐1H‐pyrazoles under mild reaction conditions using SiO2‐HNO3 as an oxidizing agent to afford 1,3,5‐trisubstituted pyrazoles with high regioselectivity. Here SiO2‐HNO3 acts as a nitrating agent along with oxidizing property. SiO2‐HNO3 is cheap, easy to prepare, eco‐friendly and practically applicable catalyst.

Direct Synthesis of Dihydropyrrolo[2,1‐a]Isoquinolines through FeCl3 Promoted Oxidative Aromatization

AbstractWe have developed a straightforward FeCl3 promoted synthesis of dihydropyrrolo[2,1‐a]isoquinolines through formal (3+2) cycloaddition/oxidative aromatization cascade of dihydroisoquinoline with Morita‐Baylis‐Hillman carbonates (up to 96% yield). Further modifications of the obtained products were successful through simple chemical transformations providing a diverse range of natural product‐like molecules (12 examples).magnified image

Cascade Functionalization of C(sp3)-Br/C(sp2)-H Bonds: Access to Fused Benzo[e]isoindole-1,3,5-trione via Visible-Light-Induced Reductive Radical Relay Strategy.

A reductive radical relay strategy for the construction of fused benzo[e]isoindole-1,3,5-trione through a reaction of α-bromo ketones with maleimides in the presence of Ir(ppy)3 under visible-light irradiation is described. The protocol employs very mild reaction conditions and offers satisfactory yields. Moreover, the reaction proceeds through a cascade C(sp3)-Br/C(sp2)-H functionalization, double C-C bond formation, and oxidative aromatization sequence.

Synthesis of N-Sulfonyl- and N-Acylpyrroles via a Ring-Closing Metathesis/Dehydrogenation Tandem Reaction

N-Sulfonyl- and N-acylpyrroles were synthesized via olefin ring-closing metathesis of diallylamines and in situ oxidative aromatization in the presence of the ruthenium Grubbs catalyst and a suitable copper catalyst. In the presence of Cu(OTf)2 and CuBr2, the reaction afforded N-sulfonyl- and N-acylpyrroles, respectively, in one pot. Under an oxygen atmosphere, the reaction went smoothly without the need of hydroperoxide oxidants. This protocol possesses many advantages, such as using a nonhazardous oxidant and readily available starting materials, operating in one pot, and showing a broad substrate scope.

Visible light mediated metal-free oxidative aromatization of 1,3,5-trisubstituted pyrazolines

The visible light mediated oxidation of 1,3,5-trisubstituted pyrazolines under metal-free conditions was developed. Various substituted pyrazolines were oxidized to pyrazoles by irradiation with visible light/sunlight. A plausible mechanism was proposed for the light mediated oxidation proceeding via formation of intermediates with electron rich C-3 positions and electron deficient C-5 positions. Correlation between the electronic effect induced by the aryl substituents and the rate of oxidation was studied by UV–vis spectroscopy. This correlation study supported the proposed mechanism. Electron withdrawing substituents at the 3-phenyl group and electron releasing substituents at the 5-phenyl group enhanced the rate of oxidation; whereas, electron donating substituents at the 3-phenyl group and electron withdrawing substituents at the 5-phenyl group reduced the rate.

Divergent Total Synthesis of Chaetoglines C to F.

The first total syntheses of chaetoglines C-F via a bioinspired and divergent synthetic strategy are reported. Chaetolines C and D were obtained from the condensation of hemiacetal and tryptophan methyl ester building blocks followed by functional group transformations. The synthesis of chaetogline E employed the diastereoselective Pictet-Spengler reaction, and the tetrahydro-carboline skeleton was further utilized as a precursor for an oxidative aromatization reaction to introduce the β-carboline moiety of chaetogline F.

Oxidative Aromatization of 3,4-Dihydroquinolin-2(1 H)-ones to Quinolin-2(1 H)-ones Using Transition-Metal-Activated Persulfate Salts.

Inorganic persulfate salts were identified as efficient reagents for the oxidative aromatization of 3,4-dihydroquinolin-2(1 H)-ones through the activation of readily available transition metals, such as iron and copper. The feasible protocol conforming to the requirement of green chemistry was utilized in the preparation of the key intermediate (7-(4-chlorobutoxy)quinolin-2(1 H)-one 2) of brexpiprazole in 80% isolated yield on a 100 g scale, and different quinolin-2(1 H)-one derivatives with various functional groups were demonstrated in 52-89% yields.

Aerobic oxidative aromatization of Hantzsch 1,4-dihydropyridines via an anomeric-based oxidation in the presence of Laccase enzyme/4-Phenyl urazole as a cooperative catalytic oxidation system

Cooperative catalytic system of Laccase enzyme (from Trametes versicolor) and 4-phenyl urazole in phosphate buffer/acetonitrile solution at 40 °C has been applied for the biomimetic aerobic oxidative aromatization of Hantzsch 1,4-dihydropyridines (1,4-DHPs) with excellent yields.

Fungal biotransformation of short-chain n-alkylcycloalkanes.

The cycloalkanes, comprising up to 45% of the hydrocarbon fraction, occur in crude oil or refined oil products (e.g., gasoline) mainly as alkylated cyclohexane derivatives and have been increasingly found in environmental samples of soil and water. Furthermore, short-chain alkylated cycloalkanes are components of the so-called volatile organic compounds (VOCs). This study highlights the biotransformation of methyl- and ethylcyclohexane by the alkane-assimilating yeast Candida maltosa and the phenol- and benzoate-utilizing yeast Trichosporon mucoides under laboratory conditions. In the course of this biotransformation, we detected 25 different metabolites, which were analyzed by HPLC and GC-MS. The biotransformation process of methylcyclohexane in both yeasts involve (A) ring hydroxylation at different positions (C2, C3, and C4) and subsequent oxidation to ketones as well as (B) oxidation of the alkyl side chain to hydroxylated and acid products. The yeast T. mucoides additionally performs ring hydroxylation at the C1-position and (C) oxidative decarboxylation and (D) aromatization of cyclohexanecarboxylic acid. Both yeasts also oxidized the saturated ring system and the side chain of ethylcyclohexane. However, the cyclohexylacetic acid, which was formed, seemed not to be substrate for aromatization. This is the first report of several new transformation reactions of alkylated cycloalkanes for eukaryotic microorganisms.

Application of laccase/DDQ as a new bioinspired catalyst system for the aerobic oxidation of tetrahydroquinazolines and Hantzsch 1,4-dihydropyridines

Laccase/DDQ as a new bioinspired quinone-based cooperative catalytic system was used for the biomimetic aerobic oxidative synthesis of 2-substituted quinazolines and Hantzsch pyridines from the oxidative cyclocondensation of 2-aminobenzylamine and aldehydes and the oxidative aromatization of 1,4-dihydropyridines, respectively. The products were obtained in good to high yields in a phosphate buffer (0.1 M, 12.5 mL, pH 4.5) and acetonitrile (4 vol%) mixture as a solvent. These methods are more eco-friendly, efficient, simple, and practical than other currently available ones because of mild reaction conditions and because they are free from any halide and toxic and expensive transition metals. Therefore, these methods can be applied in pharmaceutical and other sensitive synthetic procedures.