Oxidative Ring-opening Reaction Research Articles

Element recycling in arsoles

Abstract The incorporation of heteroatoms serves as a potent tool for the development of advanced materials, and arsenic (As) has recently become increasingly popular in the field of conjugated molecules. However, the potential toxicity of As-containing materials upon disposal remains a concern. In this study, we propose a chemical recycling approach for the As in arsoles. The oxidative ring-opening reaction of arsoles proceeds efficiently under ultraviolet irradiation, leading to the production of phenylarsonic acid, a precursor of arsoles.

Dirhodium(II)/Phosphine Catalyst with Chiral Environment at Bridging Site and Its Application in Enantioselective Atropisomer Synthesis.

A dirhodium(II)/phosphine catalyst with a chiral environment at the bridging site was developed for the asymmetric arylation of phenanthrene-9,10-diones with arylboronic acids. In contrast to the classic chiral bridging carboxylic acid (or derivatives) ligand strategy of bimetallic dirhodium(II) catalysis, in this reaction, tuning both axial and bridging ligands realized the first Rh2(OAc)4/phosphine-catalyzed highly enantioselective carbonyl addition reaction. The kinetic analysis reveals that dirhodium(II) and arylboronic acid follow the first-order kinetics, while phenanthrene-9,10-dione is zeroth-order. These data supported the proposed catalytic cycle, where the key intermediate in the rate-determining step involved the dirhodium(II) complex and arylboronic acid. Finally, axially chiral biaryls were prepared based on a newly developed oxidative ring-opening reaction of α-hydroxyl ketones with a base and molecular oxygen, which featured a central-to-axial chirality transfer radical β-scission step.

Flavin-enabled reductive and oxidative epoxide ring opening reactions

Epoxide ring opening reactions are common and important in both biological processes and synthetic applications and can be catalyzed in a non-redox manner by epoxide hydrolases or reductively by oxidoreductases. Here we report that fluostatins (FSTs), a family of atypical angucyclines with a benzofluorene core, can undergo nonenzyme-catalyzed epoxide ring opening reactions in the presence of flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (NADH). The 2,3-epoxide ring in FST C is shown to open reductively via a putative enol intermediate, or oxidatively via a peroxylated intermediate with molecular oxygen as the oxidant. These reactions lead to multiple products with different redox states that possess a single hydroxyl group at C-2, a 2,3-vicinal diol, a contracted five-membered A-ring, or an expanded seven-membered A-ring. Similar reactions also take place in both natural products and other organic compounds harboring an epoxide adjacent to a carbonyl group that is conjugated to an aromatic moiety. Our findings extend the repertoire of known flavin chemistry that may provide new and useful tools for organic synthesis.

Synthesis of 2-Hydroxy-2′-aroyl-1,1′-biaryls via Oxidative Ring-Opening of 9H-Fluoren-9-ols

An Oxone-mediated oxidative ring-opening reaction of 4,5-disubstituted 9H-fluoren-9-ols by cleavage of a carbon-carbon bond is reported. 2-Hydroxy-2'-aroyl-1,1'-biaryls can be efficiently prepared by simply heating the mixture of fluoren-9-ols, Oxone, and 1,1,1,3,3,3-hexafluoroisopropanol at 60 °C for 4 h. The persulfate-involved ring-expansion processes were proposed and supported by the DFT calculations.

A Photo- and Redox-Driven Two-Directional Terthiazole-Based Switch: A Combined Experimental and Computational Investigation.

Terthiazoles with redox-active substituents like an N-methyl pyridinium group and ferrocene have been synthesized and their photo- and electro-chromic behaviors were investigated. The presence of two lateral N-methyl pyridinium substituents in the structure of terthiazole proved to be effective in inducing not only the reductive ring-closure of the terthiazole core but also its oxidative ring-opening reaction, leading to the first terarylene-based switch able to fully operate both photochemically and electrochemically. Moreover, the large increase in the redox potential between its open and closed form (700 mV) means that a part of the photon energy necessary to trigger the cyclization is stored in the form of chemical potential available for other works. Introduction of a second redox-active unit such as ferrocene onto the central thiazolyl moiety is found to inhibit the photochromism of the switch but not its redox switchability, which, instead, got improved for the ring-opening reaction via the redox properties of the ferrocenyl unit. The optical and redox properties of the switch in its different oxidation states are analyzed with the aid of DFT calculations in order to rationalize different switching processes.

Directional Engraving within Single Crystalline Metal-Organic Framework Particles via Oxidative Linker Cleaving.

An oxidative linker cleaving (OLC) process was developed for surgical manipulation of the engraving process within single crystalline MOFs particles. The strategy relies on selective degradation of 2,5-dihydroxyterephthalic acid linker into small molecular fragments by oxidative ring-opening reactions, resulting in controllable scissoring of framework. By regulation of the generation and diffusion of oxidative species, the core MOFs will undergo divergent etching routes, producing a series of single crystalline hollow and yolk-shell MOF structures. In addition, the OLC process can be initiated and localized around the pre-embedded Pd NPs through on-site catalytic generation of oxidative species, leading to solitary confinement of multiple NPs within one single crystalline MOF particle, namely, a multi-yolk-shell structure. This unique architecture can effectively protect NPs from agglomeration while realizing size selective catalysis at the same time.

(E)-4-(3-Phenylisoxazol-5-yl)but-3-en-2-one

(E)-4-(3-Phenylisoxazol-5-yl)but-3-en-2-one was synthesized via the oxidative ring opening reaction of 2-(5-methylfuran-2-yl)-1-phenylethanone oxime, followed by the iodine mediated isomerization.

Regioselective Oxidative Ring Cleavage of Antiaromatic Nickel(II) Norcorrole to Dialkoxybis(dipyrrin)s

Invited for this month's cover is the group of Prof. Dr. Hiroshi Shinokubo at Nagoya University, Japan. The front cover shows the oxidative ring opening reaction of an antiaromatic porphyrinoid, norcorrole, into dipyrrin dimers. The background with the map of Japan represents the venue of ISNA-18, which will be held in Sapporo, Japan in July 2019. Read the full text of the article at 10.1002/cplu.201900068.

Design, synthesis and biological evaluation of a novel library of antimitotic C2-aroyl/arylimino tryptamine derivatives that are also potent inhibitors of indoleamine-2, 3-dioxygenase (IDO)

A novel library of C2-substituted tryptamines (based on diverse C2-aroyl/arylimino indoles and indole-diketopiperazine hybrids) possessing antimitotic properties were designed, synthesized and screened for their inhibitory activity against tubulin polymerization, and against proliferation of A549 lung cancer, HeLa cervical cancer, MCF7 breast cancer and HePG2 liver cancer cell lines. The design of molecules were inspired from known antimitotic compounds and natural products. The molecular docking of the designed compounds indicated that they bind to the colchicin binding site of tubulin. They were synthesized by a unique iodine catalysed oxidative ring opening reaction of 1-aryltetrahydro-β-carbolines. Among the compounds synthesized quite a few compounds induced cytotoxicity on the cancer cells by disrupting the tubulin polymerization. They were found to be non-toxic for healthy cells. Immuno Fluorescence study for the most active molecules (between ~6 μM concentration) against A549 and HeLa cells demonstrated complete disruption and shrinkage of the microtubule structures. These compounds also inhibited indoleamine-2, 3-dioxygenase with low micromolar IC50.

Application of differential reactivity towards synthesis of lamellarin and 8-oxoprotoberberine derivatives: Study of photochemical properties of aryl-substituted benzofuran-8-oxoprotoberberines

A unique differential reactivity between dihydroisoquinolines and 3-nitrocoumarins was observed and was exploited for the efficient construction of lamellarins and their isomeric benzofuran-8-oxoprotoberberine derivatives under acid-catalyzed or base-promoted conditions. Further, these prepared aryl-substituted benzofuran-8-oxoprotoberberine derivatives bearing electron-donating substituents on benzofuran moiety are found to be benchtop stable but light-sensitive, and can undergo oxidative ring-opening reaction to give the corresponding keto products when exposed to visible light under aerobic conditions.

A Facile Oxidative Opening of the C-Ring in Luotonin A and Derivatives.

An oxidative ring opening reaction of the central ring C in the alkaloid Luotonin A and two of its derivatives was found to occur upon heating with an excess amine and potassium carbonate in dimethylsulfoxide (DMSO) solution in the presence of air oxygen. The structure of the novel amide-type products was elucidated and a possible mechanism for this reaction is proposed. Four of the new compounds show moderate in vitro anticancer activity towards human colon adenocarcinoma cells.

First Total Syntheses of Tetracenomycins C and X.

The first total syntheses of tetracenomycins C and X were achieved, featuring 1) preparation of a hexasubstituted naphthonitrile oxide by successive benzyne cycloadditions and an oxidative ring-opening reaction; 2) a novel ortho-quinone mono-acetal as the A-ring unit; 3) construction of three contiguous stereogenic centers by an asymmetric benzoin cyclization, an isoxazole oxidation, and a stereoselective reduction.

Ring Opening of π-Delocalized 2,5-Diphenyltellurophene by Chemical or Self-Sensitized Aerobic Photooxidation

We report the self-sensitized aerobic photooxidation of 2,5-diphenyltellurophene (PT). Irradiation of PT induces rapid intersystem crossing to the triplet excited state, which undergoes energy transfer to oxygen to form singlet oxygen. Reaction of the heterocycle with singlet oxygen was found to occur at the carbon framework through a 1,4-cycloaddition reaction rather than at tellurium to form the Te(IV) telluroxide, as is commonly observed for other tellurium-containing heterocycles. This leads to oxidative ring-opening of the tellurophene to form (Z)-1,4-diphenylbut-2-ene-1,4-dione ((Z)-ED) with extrusion of TeO2. In attempts to study the formation of the Te(IV) telluroxide and Te(VI) tellurone by chemical oxidation with m-chloroperoxybenzoic acid (mCPBA), we discovered that PT undergoes an oxidative ring-opening reaction to the same ene-dione product after reaction with 4 equiv of mCPBA. Extrusion of TeO2 was also observed in this case. This ring-opening reaction was studied in detail by NMR spectrosco...

Attempted Synthesis and Unexpected β-Fragmentation of a Hindered β-Keto Nitroxide

The attempted synthesis of a β-keto imidazolidinone nitroxide by oxidation of the β-hydroxy imidazolidinone precursor with hydrogen peroxide and sodium tungstate led to an unexpected ring-opening reaction to produce 1,4-diazaspiro[4.5]dec-1-en-3-oxo-2-pentanoic acid 1-oxide (13) in high yield. The structure of 13 was confirmed by X-ray crystallographic analysis. A β-fragmentation mechanism is suggested for the oxidative ring-opening reaction.

Enantioselective Oxidative Ring-Opening Reaction of Aziridines with α-Nitroesters Using Cinchona Alkaloid Amide/Nickel(II) Catalysts

The enantioselective oxidative ring-opening reaction of aziridines with α-nitroacetates has been developed. Good yields and enantioselectivity were observed for the reaction of various aziridines using a novel cinchona alkaloid amide/NiBr2 catalyst. Both enantiomers of products could be obtained by using pseudoenantiomeric chiral catalysts. This process offers an efficient route for the synthesis of α-aminoketones.

ChemInform Abstract: Solvent‐Dependent Reaction Pathways Operating in Copper(II) Tetrafluoroborate Promoted Oxidative Ring‐Opening Reactions of Cyclopropyl Silyl Ethers.

Oxidative ring-opening reactions of benzene-fused bicyclic cyclopropyl silyl ethers, promoted by copper(II) tetrafluoroborate, were investigated. The regioselectivity of cyclopropane ring-opening as well as product distributions were found to be highly dependent on the nature of the solvent. In alcohols, dimeric substances arising from external bond cleavage are major products. Radical rearrangement products are also formed in solvents such as ether and ethyl acetate. On the contrary, nucleophile addition to carbocation intermediates, generated by internal bond cleavage, occurs mainly in reactions taking place in acetonitrile. It is proposed that the observed solvent effects that govern the reaction pathways followed are a consequence of varying solvation of copper intermediates, which governs their reactivity and redox properties. In addition, the influence of counteranions of the copper salts, organonitriles, cyclic dienes, and substrate structures on the pathways followed in these reactions was also ex...

Solvent-Dependent Reaction Pathways Operating in Copper(II) Tetrafluoroborate Promoted Oxidative Ring-Opening Reactions of Cyclopropyl Silyl Ethers.

Oxidative ring-opening reactions of benzene-fused bicyclic cyclopropyl silyl ethers, promoted by copper(II) tetrafluoroborate, were investigated. The regioselectivity of cyclopropane ring-opening as well as product distributions were found to be highly dependent on the nature of the solvent. In alcohols, dimeric substances arising from external bond cleavage are major products. Radical rearrangement products are also formed in solvents such as ether and ethyl acetate. On the contrary, nucleophile addition to carbocation intermediates, generated by internal bond cleavage, occurs mainly in reactions taking place in acetonitrile. It is proposed that the observed solvent effects that govern the reaction pathways followed are a consequence of varying solvation of copper intermediates, which governs their reactivity and redox properties. In addition, the influence of counteranions of the copper salts, organonitriles, cyclic dienes, and substrate structures on the pathways followed in these reactions was also examined.

ChemInform Abstract: Synthesis of Tribenzotropone by Ring Expansion of Phenanthrene‐9,10‐dione.

Tribenzotropone was efficiently synthesized by a ring-expansion method from readily available phenanthrene-9,10-dione via a ring-opened diketone as a key intermediate; the diketone was prepared by nucleophilic addition of allyl and vinyl groups, followed by an oxidative ring-opening reaction with lead(IV) acetate. Ring closure by an intramolecular Diels–Alder reaction and subsequent dehydrogenation produced tribenzotropone in 38% overall yield. Ring closure by a Morita–Baylis–Hillman reaction, on the other hand, produced a dibenzo-fused nonanedione in 22% overall yield.

An Oxidative Macrobicyclic Ring Opening of a Triptycene to a Highly Functionalized Fluorene Derivative.

The treatment of hexamethoxytriptycenes with nitric acid leads to an unprecedented oxidative ring opening of the triptycene scaffold, resulting in a new class of fluorene derivatives with a nitroquinone unit. Preliminary investigations of the influence of chain length of alkyl substituents at the triptycene bridgeheads to the reaction have been performed, revealing that exclusively the methyl-substituted hexamethoxytriptycene does not undergo an oxidative ring opening reaction.

Synthesis of Tribenzotropone by Ring Expansion of Phenanthrene-9,10-dione

Tribenzotropone was efficiently synthesized by a ring-expansion method from readily available phenanthrene-9,10-dione via a ring-opened diketone as a key intermediate; the diketone was prepared by nucleophilic addition of allyl and vinyl groups, followed by an oxidative ring-opening reaction with lead(IV) acetate. Ring closure by an intramolecular Diels–Alder reaction and subsequent dehydrogenation produced tribenzotropone in 38% overall yield. Ring closure by a Morita–Baylis–Hillman reaction, on the other hand, produced a dibenzo-fused nonanedione in 22% overall yield.