Oxidative coupling with benzoic acids

The preparation of isocoumarins from the oxidative coupling of benzoic acids with alkynes in MeOH with oxidant AgOAc is catalysed by [Cp lrCl2]2 complex. Alkyl alkynes are more reactive than aryl alkynes. The DFT calculations of intermediates and transition states reveal that C-H activation occurs via an acetate-assisted meehanism, the C-H activation is not turnover limiting and the AgOAc oxidizes the reduced form of the catalyst via an Ir(I)-lr(ll)-Ir(IIl) sequence. ... 

In 2007, the Mlura group reported a Rh(III)-catalyzed oxidative coupling of benzoic acids with internal alkynes to the synthesis of isocoumarins via aromatic C-H activation (Scheme 6.24a) [38]. Importantly, the reaction of benzoic acids with alkynes takes place efficiently even with a reduced amount (5mol%) of Cu(0Ac)2-H20 under air (Scheme 6.24b) [5b]. The same group also developed the rhodium-catalyzed coupling of acrylic acids with alkynes to provide corresponding a-pyrone via vinylic C-H bond cleavage (Scheme 6.24c) [5c]. In 2015, Wen and coworkers described a Rh(III)-catalyzed synthesis of... 

It is only very recently that rhodium-based catalytic systems have been described in efficient oxidative olefination reactions. Inspired by the work of Satoh and Miura on rhodium/copper-catalyzed aerobic oxidative coupling of benzoic acids with internal allqmes or acrylates (Scheme 9.11), Glorius and co-workers described, in 2012, a rhodium-catalyzed directing group assisted olefination of 2-aryloxazolines under air. This method, which necessitated rhodium, silver and copper metal sources, afforded the desired olefin-oxazoline products in moderate-to-good yields (Scheme 9.12). 

Benzyl chloride readily forms a Grignard compound by reaction with magnesium in ether with the concomitant formation of substantial coupling product, 1,2-diphenylethane [103-29-7]. Benzyl chloride is oxidized first to benzaldehyde [100-52-7] and then to benzoic acid. Nitric acid oxidizes directly to benzoic acid [65-85-0]. Reaction with ethylene oxide produces the benzyl chlorohydrin ether, CgH CH20CH2CH2Cl (18). Benzylphosphonic acid [10542-07-1] is formed from the reaction of benzyl chloride and triethyl phosphite followed by hydrolysis (19). 

A particularly relevant thermo-oxidative study on PET degradation and PBT reported the degradation products observed for ethylene dibenzoate [39], The products observed paralleled those of the photolysis and photo-oxidation reports discussed above with benzoic acid, vinyl benzoate, 2-hydroxyethylene dibenzoate, 2-carboxymethoxy benzoate and the coupling product, 1,4-butylene dibenzoate, being reported. The 2-hydroxyethylene dibenzoate and 2-carboxymethoxy... 

Benzoic acids yield isocoumarins through a Rh-catalysed Cu-promoted oxidative coupling with internal alkynes. When a two-fold excess of alkyne is used with Ir catalysis,... 

The reactions between i-dinitrobenzene or 1,3,5-trinitrobenzene, aryl halides, and copper(I) oxide in quinoline 17-19, 21) provide a simple synthesis of nitrobiphenyls uncontaminated by symmetrical biphenyls. These couplings may be related to the Ullmann reaction, the decarboxylative coupling of benzoic acids with aryl halides, and the preparation of ethers from phenols 165). Although no intermediates... 

The acylpalladium 141 is formed by oxidative addition of acid anhydride to Pd(0), and can be used for synthetic purposes [61]. The mixed anhydride 143 was prepared in situ by the reaction of benzoic acid with dimethyl dicarbonate (142), and the benzoylpalladium methoxide 144 is generated by decarboxylative oxidative addition of 143, and is used for Suzuki coupling with arylboronic acid to yield the diaryl ketone 145 [62]. 

Cp RhCl2]2 (Cp =pentamethylcyclopentadienyl)-catalysed ort/io-olefination of benzoic acid through oxidative coupling with alkenes using the oxidant Cu(OAc)2 has been achieved a,j8-unsaturated carboxylic acids also underwent olefination at the )3-position. Cine-olefination of heteroarene carboxylic acids progresses smoothly by decarboxylation to selectively produce the corresponding vinyl heteroarene derivatives. ... 

Hydroxyl elimination is necessary for the formation of benzaldehyde and benzoic acid derivatives and, ultimately, benzene and toluene (Fig. 7.46).2 It is proposed that a cleavage between the hydroxyl group and aromatic ring leads to benzenoid species which undergo further cleavage coupled with oxidation to give various decomposition products. 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

Only para coupling was observed during the alkaline ferricyanide oxidation of 4-hydroxy-3-(3-hydroxybenzoyl)benzoic acid. 7-Hydroxy-9-oxoxanthene-2-carboxylic acid (515) was obtained in 21% overall yield from methyl 4-hydroxybenzoate (78JCS(P1)876). The synthesis utilizes a photochemical Fries rearrangement of methyl 4-(3-methoxybenzoyloxy)benzoate to prepare the benzophenone (514 Scheme 189). A similar route was used to prepare 2-hydroxy-2 -methoxybenzophenones, which undergo intramolecular cyclization with loss of methanol on treatment with base. 

The oxidative coupling of 2-(4-hydroxyphenoxy)benzoic acid to the spiran (525) is brought about by lead(IV) oxide (61JCS2312). The spiran is converted into 2,3-diacetoxyxanthone on reaction with boron trifluoride in acetic anhydride. 

Oxidative coupling of N-benzoylpyrroles was achieved with palladium acetate. From a reaction at 110°C in acetic acid, benzopyrrolizinones (35) and 2,2 -dimeric compounds (36) were obtained. Under the same conditions 1-aroylindoles gave 37 and 38 but no 2,2 -dimeric compounds.30 Treatment of dibenzoylpyrrolizinones (37) with potassium t-butoxide/f-butyl alcohol containing a small amount of water at 82°C afforded o-(2-indo yI)benzoic acids in good yield.31... 

In a recent review it was argued that such additives of copper, benzoquinone, and HPMOV are not really needed all that is needed is the presence of oxidation-resistant ligands that prevent palladium metal formation [15]. Indeed, activation of the C-H bond is not as slow as, for example, the Wacker reaction of ethene in which reoxidation of palladium must be performed by copper oxidation, although in this catalytic system the additives may still play a role in stabilizing the intermediate low-valent palladium species and thus prevent catalyst decomposition. This thesis was corroborated by the work of de Vos and Jacobs, who showed that addition of benzoic acid to the oxidative arylation reaction in the presence of oxygen led to superior results in the coupling of a variety of substituted arenes with acrylates, cinnamates, and ,/f-unsaturated ketones. Very good yields and TON up to 762 were obtained at 90 °C. A mixture of the o, m, and p isomers is obtained if substituted arenes are used [16]. 

The selective oxidation of toluene has been studied over a number of catalysts based on metal oxides, with the U/Mo oxide system being one of the most achve and selective[50, 51]. The main products in the oxidation of toluene, excluding the non-oxidative coupling products, were benzaldehyde, benzoic acid, maleic anhydride, benzene, benzoquinone, CO and CO2. Under the same reachon condihons toluene may also yield coupling products such as phthalic anhydride, methyldi-phenylmethane, benzophenone, diphenylethanone and anthraquinone, as shown by Zhu and coworkers [51]. A range of different uranium-based oxides were tested [51] and the results obtained are shown in Table 13.4. 

In contrast to polymerisates, polycondensates can not be depolymerized under inert conditions. Decomposition usually leads to the destruction of the chemical structure and the monomers. The thermal decomposition of PET starts at about 300°C in an inert atmosphere [25]. Between 320 and 380°C the main products are acetaldehyde, terephthalic acid, and carbon oxides under liquefaction conditions. The amounts of benzene, benzoic acid, acetophenone, C1-C4 hydrocarbons, and carbon oxides increase with the temperature. This led to the conclusion that a P-CH hydrogen transfer takes place as shown in Eigure 25.8 [26]. Today the P-CH-hydrogen transfer is replaced as a main reaction in PET degradation by several analytic methods to be described in the following sections. The most important are thermogravimetry (TG) and differential scanning calorimetry (DSC) coupled with mass spectroscopy and infrared spectroscopy. 

Although a previous chapter in this volume provides a broader perspective on the reactivity of radical cations, in this section we will examine intramolecular electron-transfer reactions coupled with or followed by cleavage of a bond in odd electron species such as radical cations, radical zwitterions and radical anions. In particular, this paragraph will be divided in oxidative and reductive bond-cleavage processes. Because this field is however too large to be covered extensively here, the discussion will be limited to selected examples—for oxidative cleavages, side-chain fragmentation reactions of alkylaromatic radical cations and decarboxylation reactions of radical zwitterions derived from benzoic and arylalkanoic acids, and for reductive... 

Again, in aqueous solution, the reaction proceeds on oxidized noble metal surfaces and, at the potentials at which it takes place, the reactant anion, RCOO , is strongly adsorbed. The R must be aliphatic at the a carbon as the Kolbe reaction does not proceed if, for example, benzoic acid is the reactant however, fi-, or y-aryl alkyl carboxylic acids, for example, phenylacetic acid, will undergo the Kolbe coupling reaction but with rather poor efficiency. The reaction will also proceed on nonoxidized noble metal surfaces, for example, Pt in anhydrous CH3COOH or CF3COOH, gettered with acetic anhydride... 

A sensitive and versatile chromogenic assay for POase is based on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) and 3-(dimethylamino)benzoic acid (DMAB) (Ngo and Lenhoff, 1980) in the presence of substrate. MBTH is the donor which, after oxidation, reacts with DMAB to form a cationic in-... 

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