Arene oxidative carbonylation

Oxidative carbonylation can also be achieved by metal-assisted C - H activation. The Pd(II)-promoted oxidative carbonylation of arenes to give aromatic acids has been reported to occur under stoichiometric [127,128] as well as catalytic [129-138] conditions (Eqs. 28-30). In the case of alkylben-zenes, the Pd-catalyzed reaction shows only a moderate selectivity towards the para position. Better p-selectivilics have however been attained by employing Rh(III) or Ir(III) catalysts [139-146]. 

The intracellular nucleophile glutathione (GSH y-Glu-Cys-Gly) acts as a protective mechanism against electrophilic insults and may be present at concentrations of up to 10 mM [26]. The reaction of glutathione with a non-polar compound bearing an electrophilic carbon, nitrogen or sulfur atom may be mediated enzymatically by glutathione-S-transferase (GST), with typical substrates being species such as arene oxides, quinones and a,P-unsaturated carbonyl compounds. 

Groves et al. found that a simple heme-iodosobenzene system mimics the enzymic reactions.127 Cyclohexane and cyclohexene are oxidized to cyclohexanol and a mixture of cyclohexene oxide and cyclohexenol respectively by this system. Using meso-tetrakis-a,/J,a,/J-(o-acylamidophenyl)por-phinatoiron(III) chloride where the acyl group is (i )-2-phenylpropionyl or (S)-2 -methoxy-carbonyl-l,T-binaphthyl-2-carbonyl, optically active styrene oxides are obtained in 51% e.e. The Fe(TPP)Cl-PhIO system can also oxygenate arenes to arene oxides.128 Based on the following observations, mechanisms involving O—Felv(Por) t as the active species have been proposed (Scheme 30).127... 

The oxidative carbonylation of arenes to aromatic acids is a useful reaction which can be performed in the presence of Wacker-type palladium catalysts (equation 176). The stoichiometric reaction of Pd(OAc)2 with various aromatic compounds such as benzene, toluene or anisole at 100 °C in the presence of CO gives aromatic acids in low to fair yields.446 This reaction is thought to proceed via CO insertion between a palladium-carbon (arene) allyl chloride, but substantial amounts of phenol and coupling by-products are formed.447... 

The deoxygenation of arene oxides have also been achieved by using chromium carbonyl complexes. The aromatic hydrocarbons produced are partially converted to chromium complexes. Formation of 246 in methanol suggests Rh-catalyzed solvolysis, resulting in nucleophilic addition of meth-... 

Electric arcs, in metal vapor synthesis, 1, 224 Electric-field-induced second harmonic generation Group 8 metallocenes, 12, 109 for hyperpolarizability measurement, 12, 107 Electrochemical cell assembly, in cyclic voltammetry, 1, 283 Electrochemical irreversibility, in cyclic voltammetry, 1, 282 Electrochemical oxidation, arene chromium carbonyls, 5, 258 Electrochemical properties, polyferrocenylsilanes, 12, 332 Electrochemical reduction, bis-Cp Zr(III) and (IV) compounds, 4, 745 Electrochemical sensors biomolecule—ferrocene conjugates... 

Significant improvements have also been introduced with the use of heterogeneous catalysts that are less water-sensitive than homogeneous Lewis acids and more convenient because of easier reaction mixture work-up. An important class of MPVO solid catalysts consists of zeolite beta and its metal-containing derivatives, especially Sn-, Zr- and Ti-beta. Several examples are known and the reduction or oxidation can be performed either in the gas phase [11, 12] or in solution [13, 14]. A very recent paper also reports the use of a bifunctional Zr-beta-sup-ported Rh catalyst able to promote both arene and carbonyl reduction [15],... 

Only in a very few cases direct oxidative carbonylations of arenes have been described. For example, if naphthalene is reacted with CO and oxygen in the presence of Pd(OAc)2, naphthalene-1- and -2-carboxylic acids are obtained [69]. 

There are several classic examples of the use of FTIR spectroelectrochemistry in elucidating the EC reactions of oxidized carbonyl complexes. These include the isomerization of 17e complexes for example, the isomerization of m-[Mo(CO)2(P-P)2]+ to the trans-isomer.139 Similarly, the cis-isomer of [Re(CO)2(P P)2]+ or [Re(CO)(P—P)2X] will isomerize on oxidation as monitored in a reflection IR cell.140 One-electron oxidation of [IrH(CO)(PPh3)3] is reversible, but further oxidation to the dication induces hydride oxidation and the appearance of bands due to the 16e complex [Ir(CO)(PPh3)3]+.141 Oxidation of arene tricarbonyls of Group 6 metals is frequently irreversible, especially in coordinating solvents at ambient temperature. However, the mesitylene tungsten tricarbonyl complex is oxidized by two electrons with the reversible take up of MeCN.142... 

In an attempt to determine the atmospheric oxidation processes that would result in an arene oxide functional group in PAHs, Murray and Kong (1994) studied the reaction of particle-bound PAHs with oxidants derived from the reactions of ozone with alkenes. Phenanthrene and pyrene were converted to arene oxides under these simulated atmospheric conditions. Control experiments indicated that the oxidant responsible for the transformation was not ozone, but a product of the reaction of ozone with tetramethylethylene (TME), probably the carbonyl oxide or the dioxirane derived from TME. 

Compounds are known in the — 1 to +5 oxidation states, but the most extensive chemistry is that of /i5-cyclopentadienyl, arene and carbonyl complexes. 

In addition to the industrial apphcations, in Scheme 8.1, other reactions have been the focus of extensive research and development. For example. Chapter 12 surveys the research efforts directed toward Pd-catalyzed oxidative carbonylation of phenol affords the important monomer, diphenyl carbonate (Scheme 8.2a). Other reactions of potential industrial significance highlighted in this chapter include the oxidation of alcohols to aldehydes and ketones (Scheme 8.2b), oxidative coupling of arenes and carboxylic acids to afford aryl esters (Scheme 8.2c), benzylic acetoxylation (Scheme 8.2d), and oxidative Heck reactions (Scheme 8.2e). The chapter concludes by highlighting a number of newer research developments, including ligand-modulated catalytic oxidations, Pd/NO cocatalysis, and alkane oxidation. 

Nitrogen oxide (NO, ) cocatalysts [120] have received industrial interest in Pd-catalyzed aerobic oxidations such as oxidative carbonylation (see Section 8.2.2) [18], alkene oxidation [121], and arene acetoxylation [55]. Recent studies from academic literature have provided new insights into the roles of NO in these reactions. Pd-catalyzed aerobic alkene oxidation (Wacker reaction) typically affords methyl ketones arising from Markovnikov addition of water (or hydroxide) to an... 

In 1980 Fujiwara and colleagues described for the first time a palladium-mediated oxidative carbonylation of arenes to benzoic acids [9—11]. The direct carboxylations of benzene, toluene, anisole, chlorobenzene, furan, and thiophene were carried out under CO and in the presence of Pd(OAc)2- 2-43 % of the corresponding benzoic acids were formed as the terminal products. Later on, the reaction was performed with a catalytic amount of palladium salts using tert-... 

Scheme 6.9 Palladium-catalyzed oxidative carbonylation of arenes...

In the case of oxidative carbonylation reactions, air or other gxeen oxidants should be applied more often in these reactions, especially in the industrially relevant direct carbonylation of arenes. For the more functionalized substrates which are interesting in organic synthesis, more selective catalyst systems are needed and directing groups might be omitted in the future. 

In parallel with progress on the oxidation of alkanes to alcohols and alkyl halides have been reports on the oxidative carbonylations of alkanes and arenes to form carboxylic acids. Fujiwara showed that stoichiometric amounts of arylpalladium acetates formed from the reaction of Pd(OAc)j with arenes and that the resulting arylpalladium complex reacts with CO in acetic acid to form aromatic acids (Equation 18.22). When O, BuOOH, alkyl halides, or K SPj were added as oxidant, the reaction became catalytic in palladium, and benzoic acids were generated from benzene, CO, and the oxidant in the presence of palladium acetate (Equation 18.23). Tl-ie highest yields were obtained with KjSPg as oxidant. Sen has reported related oxidation reactions in acidic media. - ... 

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