Oxidative Aromatization Reaction Research Articles

A relay ring-closing metathesis/Diels-Alder approach to sugar-derived pluramycin-hybrids.

Herein, we present a general approach for synthesizing pluramycin hybrids, which are analogous to the pluramycinone carbocyclic skeleton. This method involves a sequence of relay ring-closing enyne metathesis, Diels-Alder and oxidative aromatization reactions to synthesize pluramycinone-sugar hybrids. As part of our ongoing research, we have successfully synthesized two pluramycin hybrid analogues by carefully monitoring the late-stage oxidative aromatization steps, which depend on the stereo-orientation of the Diels-Alder cycloadduct at the C-4 center. The undesired ring-opening product can also serve as a C-glycoside analog, providing a versatile convergent route to access both types of hybrids and highlighting the significance of this strategy.

Synthesis of Azonia Aromatic Heterocycles Bearing 6-6-6-5-6 Pentacyclic Core via Intramolecular [4 + 2]-Cycloaddition and Oxidative Aromatization Reaction Sequence in One Pot.

Cationic aza-heterocycle-fused compounds have gained wide applications in materials science, biological applications, and synthetic organic chemistry. In this report, synthesis of benzothiazolochromenopyridinium tetrafluoroborates, a novel molecular scaffold, bearing 6-6-6-5-6 pentacyclic core is described that proceeds via (i) piperidine-catalyzed Knoevenagel condensation between 2-propargyloxyarylaldehydes bearing internal alkynes and 2-benzothiazoleacetonitrile, (ii) intramolecular formal [4 + 2]-cycloaddition, and (iii) crucial molecular oxygen-mediated oxidative aromatization reaction sequence in one pot. These quaternary pyridinium salts are obtained at ambient temperature in good to high yields.

One‐Pot Synthesis of 2,3,6‐Trisubstituted Pyridines by Phosphine‐Catalyzed Annulation of γ‐Vinyl Allenoates with Enamino Esters Followed by DDQ‐Promoted Oxidative Aromatization

AbstractA one‐pot strategy for constructing trisubstituted pyridine derivatives had been established via phosphine‐catalyzed annulation and DDQ oxidative aromatization reactions. This protocol provides trisubstituted pyridines from γ‐vinyl allenoates and enamino esters under metal‐free conditions.magnified image

Chiron approach and the [4 + 2] Diels-Alder cycloaddition of 2-pyrones for the synthesis of cis-(-)-aminoindan-2-ol

A cascade Diels-Alder reaction coupled with an oxidative aromatization reaction was developed and applied to a chiral 2-pyrone for the synthesis of the relevant chiral synthon/chiral auxiliary (-)-cis-aminoindan-2-ol. Chirality and optical purity were provided by the privileged chiron 7,3-LXF.

Copper-Catalyzed N,N-Diarylation of Amides for the Construction of 9,10-Dihydroacridine Structure and Applications in the Synthesis of Diverse Nitrogen-Embedded Polyacenes.

We reported herein CuI/DMEDA catalyzed N,N-diarylation reaction of amides with various di(o-bromoaryl)methanes to produce diverse 9,10-dihydroacridine derivatives. The resulting 9,10-dihydroacridine derivatives were oxidized selectively under mild conditions to afford acridine, acridinone, and acridinium derivatives. The copper-catalyzed N,N-diarylation reaction coupled with oxidative aromatization reaction enabled the facile construction of nitrogen atom-embedded tetracenes and pentacenes of different ortho-fused patterns. The luminescence properties, especially the effect of fusion pattern on fluorescence emission of acquired N-polycenes, were also demonstrated.

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.

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.

Synthesis of Helical Quinone Derivatives by Oxidative Coupling of Substituted 2-Hydroxybenzo[c]phenanthrenes

A concise synthesis of novel substituted quinone derivatives from commercially available starting materials was developed. For this synthesis, classical photo-induced 6π-electrocyclization was utilized, followed by oxidative aromatization reaction, and subsequent oxidative coupling reactions in the presence of CuCl(OH)-TMEDA. The unique quinone derivatives were characterized by IR, 1H, and 13C NMR spectroscopies, and mass spectroscopic data analysis. In some cases, the keto dimers were obtained as significant intermediates for the quinone synthesis.

ChemInform Abstract: One‐Pot, Three‐Component Approach to the Synthesis of 3,4,5‐Trisubstituted Pyrazoles.

AbstractThe mechanistically novel one‐pot, three‐component coupling of aldehydes, dicarbonyls, and diazo compounds proceeds by a tandem Knoevenagel condensation, 1,3‐dipolar cycloaddition, and transition metal‐free oxidative aromatization reaction sequence involving the cleavage of an acetyl group for pyrazole formation.

One-pot, three-component approach to the synthesis of 3,4,5-trisubstituted pyrazoles.

An operationally simple and high yielding protocol for the synthesis of polyfunctional pyrazoles has been developed through one-pot, three-component coupling of aldehydes, 1,3-dicarbonyls, and diazo compounds as well as tosyl hydrazones. The reaction proceeds through a tandem Knoevenagel condensation, 1,3-dipolar cycloaddition, and transition metal-free oxidative aromatization reaction sequence utilizing molecular oxygen as a green oxidant. The scope of the reaction was studied by varying the aldehyde, 1,3-dicarbonyl, and diazo component individually.

Diels–Alder/Oxidative Aromatization Approach towards the All‐Carbon DEF Tricyclic Skeleton of Daphenylline

Daphenylline is a recently isolated Daphniphyllum alkaloid with an unprecedented novel hexacyclic scaffold. In this study, the synthesis of the fused all-carbon DEF tricyclic skeleton of daphenylline has been accomplished. Key steps of the reported sequence involve Evans asymmetric allylation, aldol condensation, Diels-Alder reaction, and oxidative aromatization reactions. The developed strategy might lead to the total synthesis of daphenylline.

ChemInform Abstract: Organocatalytic Triazole Formation, Followed by Oxidative Aromatization: Regioselective Metal‐Free Synthesis of Benzotriazoles.

Herein we report on our studies on the sequential one-pot combinations of amine-catalyzed multicomponent reactions (MCRs). We have developed the copper-free synthesis of functionalized bicyclic N-aryl-1,2,3-triazole and N-arylbenzotriazole products 4 and 5 from the simple unmodified starting materials through [3+2]-cycloaddition ([3+2]-CA) and oxidative aromatization reactions in one pot under amine catalysis. The sequential one-pot reaction proceeds in good yields with high selectivity by using pyrrolidine as the catalyst from the simple unmodified substrates of enones, aryl azides, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Furthermore, we have demonstrated the medicinal applications of products 4 and 5 through simple organic reactions.

Organocatalytic Triazole Formation, Followed by Oxidative Aromatization: Regioselective Metal‐Free Synthesis of Benzotriazoles

Herein we report on our studies on the sequential one-pot combinations of amine-catalyzed multicomponent reactions (MCRs). We have developed the copper-free synthesis of functionalized bicyclic N-aryl-1,2,3-triazole and N-arylbenzotriazole products 4 and 5 from the simple unmodified starting materials through [3+2]-cycloaddition ([3+2]-CA) and oxidative aromatization reactions in one pot under amine catalysis. The sequential one-pot reaction proceeds in good yields with high selectivity by using pyrrolidine as the catalyst from the simple unmodified substrates of enones, aryl azides, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Furthermore, we have demonstrated the medicinal applications of products 4 and 5 through simple organic reactions.

Bicyclization of Diazomethanes: A Synthetic Strategy for Fused Pyrazoles

AbstractOn the terminal diazo nitrogen atom, two CN bonds are formed in the bicyclization reaction of the readily available acyclic substrates with diazomethanes as 1,3‐dipoles. The tandem 1,3‐dipolar cycloaddition/intramolecular aza‐addition/oxidative aromatization reaction can tolerate a variety of functional groups and proceeds under mild metal‐free conditions to give substituted analogues of withasomnine alkaloids in good to high yields in a single step.

ANRORC rearrangement in tetrahydro-2H-chromenones. Synthesis and structural assignment by NMR, MS, X-ray and DFT calculations of 2-[3(5)-trifluoromethyl-1H-pyrazol-4-yl)arylmethyl]cyclohexenones and derivatives

This paper describes firstly the synthesis of a new series of 3-hydroxy-2-[(3(5)-(methyl/phenyl)-5(3)-(trifluoromethyl)-1H-pyrazol-4-yl)arylmethyl]-cyclohex-2-en-1-ones (2), where aryl=C6H5, 4-NO2C6H4, 4-OCH3C6H4, from an ANRORC ring transformation reaction of 3-acyl-4-aryl-2-(trifluoromethyl)-2-hydroxy-3,4,7,8-tetrahydro-2H-chromen-5(6H)-ones (1), where acyl=acetyl and benzoyl, in the presence of hydrazine hydrate, at 63–90% yields. In subsequent steps, an oxidative aromatization reaction from 2 was done in an iodine/methanol medium for the preparation of 3(5)-trifluoromethyl-5(3)-methyl-4-[(2,6-dimethoxyphenyl)-(4-methoxyphenylmethyl)]-1H-pyrazole (3) at 72% yields. Also, the alkylation reaction using benzyl chloride easily converted a pyrazole like 2 to its N-benzyl derivative (4), at 69% yield. Finally, the structural assignment of compounds 2–4 was deduced by mass spectrometry, X-ray crystal diffraction and density functional theory (DFT) calculations, which clearly and unambiguously furnished values very close to those determined from 1H, 13C and 19F NMR data.

ChemInform Abstract: Efficient Entry to Trifluoromethyl Substituted Chromanes from Oxidative Aromatization of Tetrahydro‐2H‐chromen‐5(6H)‐ones Using Iodine/Alcohol with Conventional and Microwave Methods.

Abstract This paper describes the one-pot simple and efficient oxidative aromatization reaction employing an iodine/alcohol medium for the preparation of a series of 11 new 3-acyl-2-hydroxy-5-alkoxy-4-aryl-2-(trifluoromethyl)chromanes, where acyl = Ac, Bz, furan-2-oyl; aryl = Ph, 4-NO 2 C 6 H 4 , 4-OCH 3 C 6 H 4 and alkoxy = OMe, O-Pr n , EtO and OBn from the respective 3-acyl-4-aryl-2-(trifluoromethyl)-2-hydroxy-3,4,7,8-tetrahydro-2 H -chromen-5(6 H )-ones. Yields in the range of 50–89% were obtained when the oxidative reactions were performed using both conventional thermal heating (CTH) and microwave (MW) procedures. In general, the MW method produced similar yields with shorter reaction times and easier reaction workups. As an example, a representative X-ray diffraction ORTEP for 3-benzoyl-2-hydroxy-5-methoxy-4-methoxyphenyl-2-(trifluoromethyl)chromane is also shown.

Base-Catalyzed Efficient Tandem [3 + 3] and [3 + 2 + 1] Annulation-Aerobic Oxidative Benzannulations

An efficient synthesis of substituted benzenes via a base-catalyzed [3 + 3] aerobic oxidative aromatization of α,β-unsaturated carbonyl compounds with dimethyl glutaconate was reported. All the reactions were carried out under mild, metal-free conditions to afford the products in high to excellent yields with molecular oxygen as the sole oxidant and water as the sole byproduct. Furthermore, a more convenient tandem [3 + 2 + 1] aerobic oxidative aromatization reaction was developed through the in situ generation of the α,β-unsaturated carbonyl compounds from aldehydes and ketones.

Helical Atropisomers of Strained Phenanthrenes by Photochemistry of Aromatic Pauson–Khand Cycloadducts

AbstractNorbornene and norbornadiene Pauson–Khand adducts of bis(3,5‐dimethylphenyl)acetylene and bis(3,4,5‐trimethylphenyl)acetylene were prepared. These compounds were subjected to a photochemical 6π‐electrocyclic oxidative aromatization reaction to give the corresponding phenanthrene compounds in satisfactory yield in the case of norbornene derivatives. The helical twist imposed by the methyl groups at the 3‐ and 5‐positions on the aromatic rings led to two atropisomers as a result of the non‐planar helical phenanthrene structure. The molecular structures and conformational stabilities of these atropisomers were examined by X‐ray crystallography and variable temperature NMR studies.

Efficient entry to trifluoromethyl substituted chromanes from oxidative aromatization of tetrahydro-2H-chromen-5(6H)-ones using iodine/alcohol with conventional and microwave methods

This paper describes the one-pot simple and efficient oxidative aromatization reaction employing an iodine/alcohol medium for the preparation of a series of 11 new 3-acyl-2-hydroxy-5-alkoxy-4-aryl-2-(trifluoromethyl)chromanes, where acyl=Ac, Bz, furan-2-oyl; aryl=Ph, 4-NO2C6H4, 4-OCH3C6H4 and alkoxy=OMe, O-Prn, EtO and OBn from the respective 3-acyl-4-aryl-2-(trifluoromethyl)-2-hydroxy-3,4,7,8-tetrahydro-2H-chromen-5(6H)-ones. Yields in the range of 50–89% were obtained when the oxidative reactions were performed using both conventional thermal heating (CTH) and microwave (MW) procedures. In general, the MW method produced similar yields with shorter reaction times and easier reaction workups. As an example, a representative X-ray diffraction ORTEP for 3-benzoyl-2-hydroxy-5-methoxy-4-methoxyphenyl-2-(trifluoromethyl)chromane is also shown.

Molecular Iodine—An Expedient Reagent for Oxidative Aromatization Reactions of α,β-Unsaturated Cyclic Compounds

Prompted by the scant attention paid by published literature reviews to the applications of molecular iodine in oxidative aromatization reactions, we decided to review methods developed to-date involving iodine as an oxidant to promote aromatization of α,β-unsaturated cyclic compounds.