Oxidative coupling of 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. ... 

Scheme 3.16 Pd-catalyzed oxidative coupling of benzoic acids and vinyl arenes.

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). 

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... 

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). 

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]. 

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-... 

O/t/20-arylation of benzoic acids is often preferable to ortho-arylation of benzamides if conversion of the amide moiety to other functional groups is desired. However, only a few reports have dealt with the orf/io-functionalization of free benzoic acids due to challenges that involve such transformations. The reactions can be complicated by decarboxylation of the product and the starting material. Despite those difficulties, several methods for direct o/t/io-arylation of benzoic acids have been developed. Yu has shown that arylboronates are effective in arylation of benzoic acids under palladium catalysis [59], The reactions require the presence of palladium acetate catalyst, silver carbonate oxidant, and benzoquinone. Even more interestingly, the procedure is applicable to the arylation of unactivated sp3 C-H bonds in tertiary carboxylic acids such as pivalic acid (Scheme 13) if aryl iodide coupling partner is used. Aryl trifluoroborates can also be used [60],... 

Figure 16.6-1. Synthetic and preparative applications of oxidations of acids. A, B Oxidations of benzoic acid initiated by dihydroxylation (Sects. 16.6.4.2 and 16.6.4.3) C oxidative decarboxylation (Sect. 16.6.4.1) D,E energy coupling for the regeneration of coenzymes (Sects. 16.6.2, 16.6.3).

The catalytic oxidation of toluene over metal oxides to benzaldehyde and benzoic acid are well-known industrial processes and minor amounts of coupling products are detected among the products. It is shown that the oxidative coupling of toluene is favoured under anaerobic conditions and that metal oxides of the groups III to V of the periodic table catalyse methyl-methyl coupling [1]. Pb/Li/MgO is chosen for this study because it is known as a selective catalyst for the oxidative methylation of toluene with methane [2-4] and as good benzyl radical producer [1]. 

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. ... 

The regioselective C3-alkenylation of thiophene-2-carboxylic acids was achieved via rhodium/silver-catalyzed oxidative coupling, accompanied by decarboxylation (13JOC7216). The catalyst can also be used for ort/zo-alkenylation of benzoic acids. 

The oxidative coupling of a benzoic acid with phenylboronic acid is achievable (Scheme 4.9) [13]. Thus, in the presence of a palladium catalyst together with a silver salt oxidant, decarboxylative coupling takes place selectively to produce 2,4,6-trimethoxybiphenyl. In contrast, under conditions using a copper catalyst in place of Pd, a Chan-Evans-Lam type reaction proceeds to afford phenyl 2,4,6-trimethoxybenzoate. 

In 2007, Ueura et al. reported the first effective example for oxidative coupling of aromatic substrates with alkynes through C—H bond cleavage under rhodium catalysis [22]. Thus, benzoic acids 9 and 50 react with alkynes 2 efficiently in the presence of 0.5 mol % of [Cp RhCl2]2 and 2 equiv of Cu(OAc)2 H2O in o-xylene at 100 °C to afford the corresponding isocoumarins 51 as 1 1 coupling products (Scheme 25.26) [5,22]. Five years later, the same reaction was conducted using ruthenium catalysts in place ofRh [23]. 

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. 

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... 

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. 

Miura, M. Tsuda, T. Satoh, T. Pivsa-Art, S. Nomura, M. Oxidative cross-coupling of N-(2 -phenylphenyljbenzenesulfonamides or benzoic or naphthoic acids with alkenes using a Pd-Cu catalyst system under air. J. Org. Chem. 1998, 63, 5211-5215. 

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