2-aryl 4-carboxylates

By Oxidation of a-Arylhydrazono-thioamides. The a-arylhydrazono-thioamides (10), prepared by the action of hydrogen sulphide on arylhydrazonocyanoacetic acid derivatives ArNHN=CRCN, undergo oxidative cyclization to 5-amino-2-aryl-l,2,3-thiadiazolium salts (11) (65—90%). On acetylation, they give 5-acetyl-imino-2-aryl-4-carboxylic acid derivatives (12). ... 

When an alkyl aryl ketone is heated with yellow ammonium polysulphide solution at an elevated temperature, an aryl substituted aliphatic acid amide is foimed the product actually isolated is the amide of the ci-aryl carboxylic acid together with a smaller amount of the corresponding ammonium salt of the oarboxylio acid. Thus acetophenone affords phenylacetamide (50 per cent.) and ammonium phenylacetate (13 per cent.) ... 

Band 4, 5-9411 (1683 cm. ). Aryl carboxylic acid C=0 stretching vibration (Table IV). 

Suitable starting materials for the Kolbe electrolytic synthesis are aliphatic carboxylic acids that are not branched in a-position. With aryl carboxylic acids the reaction is not successful. Many functional groups are tolerated. The generation of the desired radical species is favored by a high concentration of the carboxylate salt as well as a high current density. Product distribution is further dependend on the anodic material, platinum is often used, as well as the solvent, the temperature and the pH of the solution." ... 

Scheme 9.35 Biodihydroxylation of aryl carboxylates by mutant whole-cells.

Vinylic and aryl halides can be used to vinylate or arylate carboxylic esters (but not ketones) by the use of NiBr2 as a catalyst. " However, ketones have been vinylated by treating their enol acetates with vinylic bromides in the presence of a Pd... 

Dehydration (cf., 6, 648). A reagent (1), prepared in situ from (C6H5),PO and Tf20 in the molar ratio 2 1, effects dehydration, usually at 25°, of amides or oximes to nitriles in >90% yield. It also effects condensation of acids and amines to form amides. The reaction of an aryl carboxylic acid with an o-phenylenediamine promoted by 1 provides 2-arylbenzimidazoles in >80% yield (equation I). If the... 

Aryl methyl ketones have been obtained [4, 5] by a modification of the cobalt-catalysed procedure for the synthesis of aryl carboxylic acids (8.3.1). The cobalt tetracarbonyl anion is converted initially by iodomethane into the methyltetra-carbonyl cobalt complex, which reacts with the haloarene (Scheme 8.13). Carboxylic acids are generally obtained as by-products of the reaction and, in several cases, it is the carboxylic acid which predominates. Unlike the carbonylation of haloarenes to produce exclusively the carboxylic acids [6, 7], the reaction does not need photoinitiation. Replacement of the iodomethane with benzyl bromide leads to aryl benzyl ketones in low yield, e.g. 1-bromonaphthalene produces the benzyl ketone (15%), together with the 1-naphthoic acid (5%), phenylacetic acid (15%), 1,2-diphenylethane (15%), dibenzyl ketone (1%), and 56% unchanged starting material [4,5]. a-Bromomethyl ketones dimerize in the presence of cobalt octacarbonyl and... 

The electroreductively produced ArNi(II) XL2 (162) can lead to the corresponding aryl-carboxylates (163) [284]. Electroreduction of the arylnickel complexes (162), formed by insertion of an electrogenerated [Ni(0)L2] into aryl halide (161) (X = Br, Cl) in the presence of CO2 in a THE/HMPA-LiCl04 (or BU4NBE4) system, affords the carboxylate (163) (Scheme 66) [271-273]. 

It has been proposed that in this reaction CO2 reacts as an electrophile with [ArPd (PPh3)2] formed by reduction of the aryl-palladium(II) [102]. Aryl chlorides react too slowly with Pd° to enable an efficient carboxylation reaction. On the other hand aryl triflate and aryl bromide have similar reactivity. The synthesis of aryl carboxylic acids can then be obtained from phenols via the formation of the corresponding aryltriflate (Eq. 15) [29, 30] ... 

Cleavage of aryl carboxylates (general procedure) To a solution of NaHTe (prepared from Te (1.30 g, 10 mmol) and NaBH4 (0.90 g, 24 mmol) in EtOH (20 mL)) buffered with AcOH (1.2 ml) in EtOH (5 ml.) is added the aryl carboxylate (5 mmol). The mixture is refluxed for 30 min, poured into ice-H20 (200 mL), extracted with CHCI3 and the... 

Model Compounds. Model compounds were employed to provide well known materials to study specific chemical reactions or to provide standards to calibrate the analytical techniques. These included 1-naphthoic acid and 2-naphthoic acid to study the reaction of aryl carboxyl groups under preliquefaction conditions. 

Rhodium(II) forms a dimeric complex with a lantern structure composed of four bridging hgands and two axial binding sites. Traditionally rhodium catalysts faU into three main categories the carboxylates, the perfluorinated carboxylates, and the carboxamides. Of these, the two main bridging frameworks are the carboxylate 10 and carboxamide 11 structures. Despite the similarity in the bridging moiety, the reactivity of the perfluorinated carboxylates is demonstrably different from that of the alkyl or even aryl carboxylates. Sohd-phase crystal structures usually have the axial positions of the catalyst occupied by an electron donor, such as an alcohol, ether, amine, or sulfoxide. By far the most widely used rhodium] 11) catalyst is rhodium(II) acetate [Rh2(OAc)4], but almost every variety of rhodium] 11) catalyst is commercially available. 

Oxidation of an alkylated benzene (making an aryl carboxylic acid) is a method of converting an ortho-para activator into a meta director. The reduction of a nitro group to make an aryl amine is a way of changing a meta director into an ortho-para activator. 

Tetrakis-/i-(carboxylato)-dimolybdenum(II) complexes have been obtained by only one general route, namely by the direct interaction of carboxylic acids with molybdenum hexacarbonyl.8 This reaction requires elevated reaction temperatures and prolonged reaction times. These same compounds are obtained in comparable or better yields by the brief reaction of tetrachloro- or tetrabromotetrakis(tributylphosphine)dimolybdenum(II) with alkyl- or aryl-carboxylic acids in refluxing benzene. The bis-/i-(arylcarboxylato) complexes... 

ProMem 10.35 Which isomer of the arene C,oH,4 resists vigorous oxidation to an aryl carboxylic acid ... 

The rearrangement occurs more readily when activating groups (aryl, carboxyl, etc.) are attached to the triple bond. Jacobs [38] reports that a reaction involving adsorption of an acetylenic compound on an active basic surface has led to the practical synthesis of arylallenes, allenyl ethers, allenyl halides, and other substituted allenes. 

Vinylic and aryl halides can be used to vinylate or arylate carboxylic esters (but not ketones) by the use of NiBr2 as a catalyst.1463 However, ketones have been vinylated by treating their enol acetates with vinylic bromides in the presence of a Pd compound catalyst.1464 Also as in 0-94, this reaction can be used to close rings.1465 In one example of this, rings have been closed by treating a diion of a dialkyl succinate with a l,cu-dihalide or ditosylate,1466, e.g. ... 

Diaryl ketones.2 In the presence of this complex (1 equivalent) S-(2-pyridyl) aryl thioates (1 equivalent), prepared from aryl carboxylic acids, undergo reductive homocoupling to diaryl ketones (equation I). 

ArenecarboxyHc acids.1 Aryl diazonium tetrafluoroborates react with carbon monoxide in the presence of catalytic amounts of Pd(OAc)2 to give aryl carboxylic acids in 70-85% yield. 

When the nickel complexes [NiX2(PPh3)2] (X = Cl, Br) are reduced electrochemically in the presence of C02 and aryl halides, aryl carboxylate anions are formed.585 The reduction leads to nickel(O) complexes which then undergo oxidative addition of the aryl halide followed by insertion of C02. Further reduction then gives the product and regenerates nickel(O) (Scheme 55). 

The surprising occurrence of photoionization in aryl carboxylic acids may be explained by the transfer of excitation energy from the ring system to the carboxyl group to give an intermediate with charge separation at the side-chain terminus—e.g.,... 

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