Carbon-oxygen Bond Formation Research Articles

Synthesis of Oxazoles from Enamides via Phenyliodine Diacetate-Mediated Intramolecular Oxidative Cyclization

A group of functionalized oxazoles were synthesized in moderate to good yields from enamides via phenyliodine diacetate (PIDA)-mediated intramolecular cyclization. The main advantageous features of the present method include its broad substrate scope and the heavy-metal-free characteristic of the oxidative carbon-oxygen bond formation process.

Catalyst-free synthesis of coumarin-, quinolone- and pyridine-annulated oxazole derivatives

An efficient approach for the synthesis of coumarin-, quinolone- and pyridine-annulated oxazole derivatives has been achieved by direct base-mediated intramolecular carbon–oxygen bond formation in a transition metal catalyst-free protocol. Intramolecular cyclization of o-bromoamides in DMSO in the presence of Cs2CO3 at 130°C affords heterocycle-annulated oxazole derivatives in high yields via a nucleophilic addition of amide to form the C–O bond.

分子状酸素を用いる炭素-酸素結合生成反応—効率的な酸素官能基導入反応—

Carbon-oxygen bond formation reaction is one of the most important methods in organic synthesis. In recent years some efficient oxidations using molecular oxygen have been reported. In this review, catalytic methods using copper or palladium complexes and metal-free radical method for installing oxygen-functionality are discussed.

Orthometallation as a Strategy in Pd-mediated Organic Synthesis

The orthopalladated complexes are among the most representative Pd(II) compounds. They display a wide prospect of applications, but they are mainly known by their use as intermediates in metal-mediated organic synthesis. In this review we describe how palladacycles are used to build up new molecules through regioselective formation of C-halogen, C-O, C-N, C-P, C-S and C-C bonds, either under catalytic or stoichiometric conditions. This methodology is based on the selective incorporation of the Pd into the organic skeleton to be modified and subsequent reactivity of the Pd-C bond toward different substrates. In many cases this strategy is alternative or even competitive, improving standard organic methods. The most recent achievements of the last five years will be covered here, presenting only the most impressive results. Keywords: CH activation, orthopalladation, palladium, insertion, oxidative coupling, CARBON-HALOGEN BOND FORMATION, CARBON-OXYGEN BOND FORMATION, CARBON-NITROGEN BOND FORMATION, ARYLATIONS, dibenzofurans, methyloximes, heteroarenes, norbornene, organometallic reagent, disulfide intermediate

Total Synthesis of Optically Active Lycopladine A by Utilizing Diastereoselective Protection of Carbonyl Group in a 1,3-Cyclohexanedione Derivative

We successfully synthesized two enantiomers of bicyclic enones, (7R,7aR)- and (7S,7aS)-9, from the hemiacetal 2a, which we first synthesized from the symmetrical diketone 1a via diastereoselective carbon-oxygen bond formation between one of the carbonyl groups and the chiral alcohol on the C2 side chain in a 2,2-disubstituted 1,3-cycloalkanedione derivative. We also report the total synthesis of natural (+)-lycopladine A [(+)-6] from (7R,7aR)-9 and the formal synthesis of unnatural (-)-lycopladine A [(-)-6] from (7S,7aS)-9.

ChemInform Abstract: Direct Transition‐Metal‐Free Intramolecular C—O Bond Formation: Synthesis of Benzoxazole Derivatives.

A direct base-mediated intramolecular carbon-oxygen bond formation has been developed without a transition-metal catalyst. In the presence of 2.0 equiv of K2CO3 in DMSO at 140 °C, the intramolecular cyclization of o-haloanilides affords benzoxazoles in high yields. A mechanism via an initial formation of a benzyne intermediate followed by nucleophilic addition to form the C–O bond has been proposed.

Direct transition-metal-free intramolecular C–O bond formation: synthesis of benzoxazole derivatives

A direct base-mediated intramolecular carbon-oxygen bond formation has been developed without a transition-metal catalyst. In the presence of 2.0 equiv of K(2)CO(3) in DMSO at 140 °C, the intramolecular cyclization of o-haloanilides affords benzoxazoles in high yields. A mechanism via an initial formation of a benzyne intermediate followed by nucleophilic addition to form the C-O bond has been proposed.

Analysis of the Ring-Closing of Chloride Polyether Polyol by the Method of Quantum Chemical Calculating

The ring-closing reaction of chloride polyether polyol was calculated by Gaussian03 software. The Density Function Theory (DFT) method were employed to study the geometry structures of chloride polyether polyol and the product was obtained on the base of B3LYP/6-31G+ model in this paper. The transitional states (Ts1, Ts2) during the ring-closing process were found by TS method and the energy changing of the system was proved by IRC calculation. Results showed that the ring-closing of chloride polyether polyol had two transition states: hydrogen transferring and the formation of new carbon-oxygen bond. The total energy of reactants was -1459.99627a.u and product is -1460.31170 a.u. The energy of the system was reduced by 175.47621kJ/mol. The ring-closing of chloride polyether polyol was exothermic and stable in thermodynamics.

Palladium- and Copper-Catalyzed Aryl Halide Amination, Etherification and Thioetherification Reactions in the Synthesis of Aromatic Heterocycles

This article reviews the use of palladium- and copper-catalyzed aryl halide amination, etherification and thioetherification processes in the synthesis of heteroaromatic molecules. The review is structured by the nature of the key C-X bond being formed, and then by heterocycle type. Where applicable individual heterocycles are further divided into syntheses based on intermolecular, intramolecular and cascade processes. In order to limit the length of the article, processes that do not deliver an aromatic heterocycle from the key C-X bond-forming event are excluded. Processes for the functionalization of intact heteroaromatics are also not included. 1 Introduction 2 Carbon-Nitrogen Bond Formation 2.1 Indoles 2.2 Carbazoles 2.3 Benzimidazoles and Benzimidazolones 2.4 Indazoles and Indazolones 2.5 Pyrroles 2.6 Pyrazoles 2.7 Oxazoles 2.8 Quinolones 2.9 Quinazolines, Quinazolinones and Quinazolinediones 2.10 Phenazines 2.11 Cinnolines 3 Carbon-Oxygen Bond Formation 3.1 Benzofurans 3.2 Benzoxazoles 3.3 Isocoumarins 4 Carbon-Sulfur Bond Formation 4.1 Benzothiophenes 4.2 Benzothiazoles 4.3 Oxathioles 5 Conclusion. © Georg Thieme Verlag Stuttgart · New York.

The CO Formation Reaction Pathway in Steam Methane Reforming by Rhodium

Three different pathways toward CO formation from adsorbed CH and O are compared by quantum-chemical density functional theory (DFT) calculations for planar and stepped Rh surfaces. The conventional pathway competes with the pathway involving a formyl (CHO) species. This holds for both types of surfaces. The barrier for carbon-oxygen bond formation for the planar surface (180 kJ/mol) is substantially higher than that for the stepped surface (90 kJ/mol). The reaction path through intermediate formyl formation competes with direct formation of CO from recombination via adsorbed C and O atoms. Calculations are used as a basis for the analysis of the overall kinetics of the methane steam reforming reaction as a function of the particle size and the metal.

Engineering of Enzymes for Selective Catalysis

Naturally occurring enzymes are truly remarkable catalysts. However, many are not suitable for practical synthetic chemistry because of poor substrate or product selectivity. This review highlights recent advances in engineering enzymes for selective catalysis. Selected topics include altering substrate specificity, altering substrate and product selectivity, engineering enzymes that catalyze carboncarbon bond formation or carbon-oxygen bond cleavage and formation, and engineering multi-function enzymes such as polyketide synthases. Keywords: Directed evolution, enzyme engineering, biocatalysis, selectivity, Enzymes, biocatalysts, epPCR, DNA shuffling, StEP, enantioselectivity, regioselectivity, polyketide synthases, Cytochrome P450 monooxygenases, Bacillus megaterium, FAD, (FMN), NADPH, NADH, UTP, UGPase, (UNGPase), creatine kinase, glycocyamine kinases, E.coli, B.megaterium, C3-C8, MAO-N, Pseudomonas aeruginosa, FDH, Candida boidinii, (PTDH), Pseudomonas stutzeri, TSSM, XR, FDA, HPLC, CASTing, L-methionine, hydantoinase, L-enantiomer, GeneReassembly, cytochrome P450 2B1, (C-C) bond formation, DERA, Lipitor, (NAL), BFD, Pseudomonas putida, Glycosidases, Polyketides, Type I PKSs, Type II PKSs, Type III PKSs, (TAL), FACS

ChemInform Abstract: Electroorganic Reactions. Part 35. Efficient Carbon-Oxygen Bond Formation in the Anodic Coupling of Pyridopyrimidine Derivatives.

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Nano‐Cu2O‐Catalyzed Formation of CC and CO Bonds: One‐Pot Domino Process for Regioselective Synthesis of α‐Carbonyl Furans from Electron‐Deficient Alkynes and 2‐Yn‐1‐ols

The formation of carbon-carbon and carbon-oxygen bonds continues to be an active and challenging field of chemical research. Nanoparticle catalysis has attracted considerable attention owing to its environmentally benign and high activity toward the reactions. Herein, we described a novel and effective nano-Cu(2)O-catalyzed one-pot domino process for the regioselective synthesis of α-carbonyl furans. Various electron-deficient alkynes with 2-yn-1-ols underwent this process smoothly in moderate to good yields in the presence of air at atmospheric pressure. It is especially noteworthy that a novel 2,4,5-trisubstituted 3-ynylfuran was formed in an extremely direct manner without tedious stepwise synthesis. Additionally, as all of the starting materials are readily available, this method may allow the synthesis of more complex α-carbonyl furans. An experiment to elucidate the mechanism suggested that the process involved a carbene intermediate.

Tandem Reactions of 2-Methylimidazoline and 1,2-Dimethylimidazoline with Various Benzoyl Chlorides

The reactions of 2-methylimidazoline with excess benzoyl chlorides under mild conditions generated N,N′-diacyl-β-keto cyclic ketene-N,N′-acetals. Conversely, the corresponding reactions of 1,2-dimethylimidazoline under the same conditions stereoselectively formed the ring-opened (Z)-vinyl benzoates. The latter reactions feature the formation of carbon-carbon bonds, carbon-nitrogen bonds, and carbon-oxygen bonds in one sequential cascade.

Metal-Catalyzed Heterocyclization: Formation of Five- and Six-Membered Oxygen Heterocycles through Carbon-Oxygen Bond Forming Reactions

This review describes the synthesis of five- and six-membered oxygen heterocycles through carbon-oxygen bond formation by metal catalyzed heterocyclization published during 2005 to 2008.

Start Smart

Palladium(0) complexes are widely used as homogeneous catalysts for formation of carbon-carbon, carbon-oxygen, and carbon-nitrogen bonds. In general, the active catalysts are too unstable to store, and so precursors [often in the Pd(II) oxidation state] are prepared with stabilizing ligands that dissociate under the reaction conditions. However, the mechanisms and efficiency whereby these precursors transform into active catalysts have largely gone unaddressed, as has the potentially inhibitory effect of the stabilizing ligands left behind in the reaction solution. Biscoe et al. undertook a more careful approach by synthesizing a stable Pd(II) precursor complex resembling a reaction intermediate along the catalytic cycle. In three efficient steps, they appended a cyclometalated phenyl ring with a tethered chelating amine group to the Pd center. Exposure of this precatalyst to basic reaction conditions in the presence of aryl chlorides and amines led to rapid liberation of the protective ligand as an inert dihydroindole, leaving the resultant Pd(0) complex free to proceed with a similar C-N coupling cycle of the bulk reagents. In comparison with traditional precatalysts, these complexes dramatically accelerated coupling reactions (in one case from 4 days to 4 hours), allowing loadings below 1 mol % and reaction temperatures at or below 25°C for sensitive substrates. The absence of interfering precatalyst ligands also facilitated clear mechanistic studies. — JSY

Dynamic Effects on Reaction Rates in a Michael Addition Catalyzed by Chalcone Isomerase. Beyond the Frozen Environment Approach

We present a detailed microscopic study of the dynamics of the Michael addition reaction leading from 6'-deoxychalcone to the corresponding flavanone. The reaction dynamics are analyzed for both the uncatalyzed reaction in aqueous solution and the reaction catalyzed by Chalcone Isomerase. By means of rare event simulations of trajectories started at the transition state, we have computed the transmission coefficients, obtaining 0.76 +/- 0.04 and 0.87 +/- 0.03, in water and in the enzyme, respectively. According to these simulations, the Michael addition can be seen as a formation of a new intramolecular carbon-oxygen bond accompanied by a charge transfer essentially taking place from the nucleophilic oxygen to the carbon atom adjacent to the carbonyl group (C (alpha)). As for intermolecular interactions, we find a very significant difference in the evolving solvation pattern of the nucleophilic oxygen in water and in the enzyme. While in the former medium this atom suffers an important desolvation, the enzyme provides, through variations in the distances with some residues and water molecules, an essentially constant electric field on this atom along the reaction progress. Grote-Hynes (GH) theory provides a useful framework to systematically analyze all the couplings between the reaction coordinate and the remaining degrees of freedom. This theory provides transmission coefficients in excellent agreement with the Molecular Dynamics estimations. In contrast, neither the frozen environment approach nor Kramers theory gives results of similar quality, especially in the latter case, where the transmission coefficients are severely underestimated. The (unusual) failure of the frozen environment approach signals the importance of some dynamical motions. Within the context of GH theory, analysis of the friction spectrum obtained in the enzymatic environment, together with normal-mode analysis, is used to identify those motions, of both the substrate and the environment, strongly coupled to the reaction coordinate and to classify them as dynamically active or inactive.

Structure‐reactivity relationships for β‐galactosidase (Escherichia coli, lac Z): a second derivative effect on βnuc for addition of alkyl alcohols to an oxocarbenium ion reaction intermediate

Velocities for the synthesis of trifluoroethyl 2-deoxy-β-D-galactopyranoside by transfer of the 2-deoxygalactosyl group from β-galactosidase to trifluoroethanol were determined from studies of the β-galactosidase-catalyzed cleavage of 4-nitrophenyl-2-deoxy-β-D-galactopyranoside as the difference in rates of appearance of 4-nitrophenoxide anion and 2-D-deoxygalactose. These data were used to calculate a rate constant ratio of k(ROH)/k(s) = 2.3 M(-1) for partitioning of the intermediate between addition of trifluoroethanol and solvent water. Velocities for the synthesis of other alkyl 2-deoxy-β-D-galactopyranosides by transfer of the 2-deoxygalactosyl group from β-galactosidase to alkyl alcohols were determined from the effect of alkyl alcohols on the velocity of β-galactosidase-catalyzed cleavage of 4-nitrophenyl-2-deoxy-β-D-galactopyranoside in a reaction where breakdown of the intermediate is rate determining. These data were used to calculate rate constant ratios k(ROH)/k(s) for the reactions of eight alkyl alcohols. Absolute rate constants k(ROH) (M(-1) s(-1)) were calculated from k(ROH)/k(s) and k(s) = 0.002 s(-1) for the addition of water. A Brønsted coefficient of β(nuc) = -0.07 ± 0.08 was determined as the slope of a logarithmic correlation of k(ROH) against alcohol pK(a). The change from a 2-OH to a 2-H substituent at the β-D-galactopyranosyl intermediate causes a 0.12 ± 0.04 increase in the value of β(nuc) for alcohol addition. This anti-Hammond effect provides evidence that general basecatalyzed addition of alcohols to an enzyme bound β-D-galactopyranosyl oxocarbenium ion intermediate proceeds along a reaction coordinate in which there is strong coupling between carbon-oxygen bond formation and proton transfer from the alcohol to a basic residue at the enzyme.

Manganese(III) Acetate: A Versatile Reagent in Organic Chemistry

Free radical reactions have become increasingly important, as well as a very attractive tool, in organic synthesis within the last two decades, due to their powerful, selective, specific, and mild reaction abilities. Mn(OAc)3 mediated oxidative free radical reactions have been extensively developed in the last twenty years. Numerous regio-, chemo-, and stereoselective synthetic methods have been developed in both inter- and intramolecular reactions, and have detailed the progress of Mn(OAc)3 mediated oxidative free radical reactions since the end of the 19th century. The new literature about the new synthetic methods on Mn(OAc)3 mediated carbon-carbon bond formation and carbon-oxygen bond formation reactions has not been extensively reviewed. The present paper summarizes the recent developments in oxidative free radical reactions mediated by Mn(OAc)3. Mn(OAc)3 mediated reactions of conjugated systems (e.g., alkenes, alkynes, 1,3-alkadienes, l,3-alkadiynes, 1-alken-3-ynes) with β-dicarbonyl compounds, Mn(OAc)3 mediated alkylation, such as the oxidative addition of an aldehyde or ketone to alkenes, Mn(OAc)3 mediated free-radical cyclization of alkenes with active methylene compounds in the presence of oxygen to afford the cyclic peroxides; lactone synthesis by the Mn(OAc)3 mediated oxidative addition of carboxylic acids to alkenes, Mn(OAc)3 mediated cyclization of α- (methylthio)acetamides, enamides, and β-keto carboxamides to afford cyclic products. Mn(OAc)3 oxidative free-radical cyclizations of allylic β-dicarbonyl compounds, for example, the cyclization of allylic β-ketoesters to afford the corresponding γ-lactone. The reaction of alkenes with sodium azide in the presence of acetic acid was investigated to Keywords: Free radical reactions, Lactone synthesis, Cycloperoxidation, Oxidative Cyclization, Carbon-Oxygen Bond Formation

Carbon-oxygen bond formation by fungal laccases: cross-coupling of 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide with the solvents water, methanol, and other alcohols

Laccase-catalyzed reactions lead to oxidation of the substrate via a cation radical, which has been described to undergo proton addition to form a quinonoid derivative or nucleophilic attack by itself producing homomolecular dimers. In this study, for the substrate 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide, we show that, besides the quinonoid form of substrate, all products formed are nonhomomolecular ones. Indeed, without addition of a reaction partner, heteromolecular products are formed from the quinonoid form of the laccase-substrate and the solvents water or methanol present in the incubation assay. Consequently, in laccase catalyzed syntheses performed in aqueous solutions or in the presence of methanol or other alcohols, undesirable heteromolecular coupling reactions between the laccase substrate and solvents must be taken into account. Additionally, it could be shown at the example of methanol and other alcohols that C-O-bound cross-coupling of dihydroxylated aromatic substances with the hydroxyl group of aliphatic alcohols can be catalyzed by fungal laccases.