Palladium aromatic acids

Simple l,2,3,4-tetrahydro-)3-carbolines have been aromatized in this manner. Palladium black at 160-170° or at higher temperature, palladium-maleic acid in aqueous solution, and platinum/oxygen have been used for the purpose. Palladium-on-charcoal in a high-boiling solvent has been used also to aromatize 5,6,7,8-tetrahydro-j3-carbohnes and 6,7,8,9-tetrahydro-3-carbo-hne. ... 

The palladium-catalyzed carbonylation of aryl halides in the presence of various nucleophiles is a convenient method for synthesizing various aromatic carbonyl compounds (e.g., acids, esters, amides, thioesters, aldehydes, and ketones). Aromatic acids bearing different aromatic fragments and having various substituents on the benzene ring have been prepared from aryl iodides at room temperature under 1 atm... 

In the palladium-catalyzed coupling reactions of arenes with alkenes, the cr-arylpalladium complexes react with CO to give aromatic acids in AcOH, as shown in Scheme u 97>97a 97c This carboxylation reaction of arenes with CO proceeds catalytically with respect to Pd at room temperature under atmospheric pressure of CO, when K2S2O8 is added as an oxidant and TFA is employed as a solvent. 

Aromatic acid chlorides are converted into the corresponding anhydrides in high yields (>95%), when reacted with carbon monoxide under solid liquid basic catalysed conditions in the presence of a complexed cobalt or palladium salt [6]. In the absence of the quaternary ammonium salt, only hydrolysis to the carboxylic acid occurs. 

Perhaps the most industrially feasible approach has been developed by Rich and co-workers at General Electric, a palladium-catalyzed silylative decarbonylation reaction of aromatic acid chlorides with disilanes [Eq. (35)].97 One of the silicon centers from the disilane is transferred to the arene whereas the other acts as a chloride acceptor to produce the chlorosi-... 

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... 

Aromatic acid chlorides are decarbonylated to aryl chlorides when they are heated to 300-360 C with palladium on carbon. The reaction proceeds by way of an aroylpalladium chloride, then to an arylpalla-dium chloride and finally through a reductive elimination to the aryl chloride. If the reaction is conducted in the presence of a reactive alkene under mild conditions the aroylpalladium chloride intermediate will sometimes acylate the alkene, as noted in Section 4.3.5.3.I. More usually, however, decarboxylation is more rapid than acylation, especially at higher temperatures (>100 C), and decarbonylation occurs. The... 

Bumagin, N. A., Gulevich, Y. V., Beletskaya, I. P. Palladium-catalyzed synthesis of aromatic acid derivatives by carbonylation of aryl iodides and AlkjSnNu (Nu = MeO, Et2N, PhS, EtS). J. Organomet. Chem. 1985, 285, 415-418. 

The carbonylation of chloroarenes has been described by Alper and Grushin [27] and Jenner and Bentaleb [28], While the former showed that square-planar complexes of divalent palladium, [ L2PdCl2], where L = tertiary phosphine, are active catalysts for the biphasic carbonylation of aromatic halides, including chloroarenes (when L = tricyclohexylphosphine), to the corresponding carboxylic acids, the latter demonstrated that chloroarenes can be converted into aromatic acids via catalytic reaction with aqueous methyl formate under biphasic conditions. [ PdCl2(PCy3)2] was the most efficient catalyst. The addition of [ Ru3(CO)12] and ammonium formate improved yield and selectivity of the carbonylation reaction. The mechanism should involve oxidative addition of the C—Cl bond to a zero-valent Pd species followed by CO insertion. However, the palladium catalyst may also directly activate methyl formate. Compared to other carbonylations of aryl-Hal compounds the procedure is quite convenient (no solvent, no initial pressurization) [27]. 

Meyers et al. reported that arylpalladium intermediates are generated from electron-rich aromatic acids 88 by decarboxylation and undergo HR in 5 % DMSO-DMF when palladium trifluoroacetate was used. However, addition of 3 equivalents of Ag2C03, which may accelerate the decarboxylation, is necessary [58]. 

Palladium catalysis is also crucial to the success of enone preparation by the reaction of aromatic acid chlorides with... 

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. - ... 

Palladium-phosphinous acids (POPds), either isolated or generated in situ, are also able to catalyze the cross-coupling of aromatic organozinc reagents and aryl chlorides [134]. It is assumed that deprotonation of the hydroxy group by the zinc... 

The carbonylation reaction was carried out by mixing an aqueous solution of NaOH with a xylene solution of the Pd(PPh3)4 in the presence of salt, PhCH2NEt3Cl. Tilley reported the synthesis of anthranilic acid using this method. Pd-catalyzed carbonylation of 2-bromoaniline did not afford anthranilic acid 2e (Scheme 6), but N-acetylated 2-bromoaniline la afforded the desired A -acetylanthranilic acid 2a in high yield. Carbonylation of aqueous media under 1 atm pressure in the presence of palladium complexes without phosphine ligand and some bases leads to the formation of aromatic acid. ... 

During the development of this arylation reaction, it was found that the rr-aryl-Palladium complexes reacted with CO to give aromatic acids, when AcOH was used as a solvent (Scheme... 

Pd-Catalyzed Reactions in the Presence of Ag Salts A bimetallic system containing a Pd catalyst has been used in some cases to achieve Ar-Ar bond formation. Palladium-mediated decarboxylative cross-coupling of aromatic acids and aryl iodides takes place efficiently under microwave heating (MW), affording the corresponding biaryls, as shown in Scheme 22.40 (path a) [55]. 

Voutchkova, A., Coplin, A., Leadbeater, N. E., Crabtree, R. H. (2008). Palladium-catalyzed decarboxylative coupling of aromatic acids with aryl halides or unactivated arenes using microwave heating. Chemical... 

Allylic and aromatic acid halides have been obtained using palladium catalysts [39, 40]. In the presence of sodium fluoride aromatic chlorides can directly be converted into acid fluorides but yields and selectivities are low despite severe reaction conditions [41]. 

Acylindoles, with palladium acetate and sodium peroxydisulphate under a carbon monoxide atmosphere, give l-acylindole-3-carboxylic acids. Palladium-promoted formation of aromatic acids from aromatic compounds with carbon monoxide has been reported previously. 

It has been reported that the reaction of aromatic compounds with sodium palladium(II) malonate in a mixed solvent of acetic acids and acetic anhydride or carbon tetrachloride gives aromatic acids in good yields, together with lower yields of aromatic dimers. 

NMR signals of the amino acid ligand that are induced by the ring current of the diamine ligand" ". From the temperature dependence of the stability constants of a number of ternary palladium complexes involving dipeptides and aromatic amines, the arene - arene interaction enthalpies and entropies have been determined" ". It turned out that the interaction is generally enthalpy-driven and counteracted by entropy. Yamauchi et al. hold a charge transfer interaction responsible for this effect. 

Trichloroacetic acid K = 0.2159) is as strong an acid as hydrochloric acid. Esters and amides are readily formed. Trichloroacetic acid undergoes decarboxylation when heated with caustic or amines to yield chloroform. The decomposition of trichloroacetic acid in acetone with a variety of aUphatic and aromatic amines has been studied (37). As with dichloroacetic acid, trichloroacetic acid can be converted to chloroacetic acid by the action of hydrogen and palladium on carbon (17). 

Polymerization by G—G Goupling. An aromatic carbon—carbon coupling reaction has been employed for the synthesis of rigid rod-like polyimides from imide-containing dibromo compounds and aromatic diboronic acids ia the presence of palladium catalyst, Pd[P(CgH )2]4 (79,80). 

This reaction is favored by moderate temperatures (100—150°C), low pressures, and acidic solvents. High activity catalysts such as 5—10 wt % palladium on activated carbon or barium sulfate, high activity Raney nickel, or copper chromite (nonpromoted or promoted with barium) can be used. Palladium catalysts are recommended for the reduction of aromatic aldehydes, such as that of benzaldehyde to toluene. 

Displacement of aromatic halogen in 2,4-diiodo-estradiol with tritiated Raney nickel yields 2,4-ditritiated estradiol. Aromatic halogen can also be replaced by heating the substrate with zinc in acetic acid-OD or by deuteration with palladium-on-charcoal in a mixture of dioxane-deuterium oxide-triethylamine, but examples are lacking for the application of these reactions in the steroid field. Deuteration of the bridge-head position in norbornane is readily accomplished in high isotopic purity by treatment of the... 

Perhaps the most reliable method for the reductive cyclization of a nitro ester to a hydroxamic acid is that which involves treatment with sodium horohydride in the presence of palladium on charcoal. Although under these conditions aromatic nitro compounds are reduced to amines, o-nitro esters such as 53, in which the ester group is suitably oriented with respect to the nitro group, give good yields of cyclic hydroxamic acids (54). Coutts and his co-... 

Hydrogenolysis of aromatic carbonyls occurs mainly by conversion to the benzyl alcohol and its subsequent loss. If hydrogenolysis is desired, the usual catalyst is palladium 38). Hydrogenolysis is facilitated by polar solvent and by acid (55). For instance, hydrogenation of 3,3-dicarbethoxy-5,8-dimethoxy-l-tetralone (5) over 5% Pd-on-C gave 6 quantitatively 54) when hydrogen absorption ceased spontaneously. 

An unusual by-product was obtained in small yield in palladium-catalyzed reduction of 2-amino-4,5-dimethoxyindanone hydrochloride, The reduction was done in two stages first, a rapid absorption of 1 mol of hydrogen at 38 C to give the amino alcohol, and then a much slower reduction in the presence of HCIO4 at 70 "C. The rearranged by-product was shown to arise from attack of acid on the amino alcohol (50), Resistance to hydrogenolysis is characteristic of / -amino aromatic alcohols (56), a fact that makes reduction of aromatic oximino ketones to amino benzyl alcohols a useful synthetic reaction. 

The above generalities apply particularly to palladium. Hydrogenation over platinum or rhodium are far less sensitive to the influence of steric crowding. Reduction of 1-t-butylnaphthalene over platinum, rhodium, and palladium resulted in values of /ci//c2 of 0.42, 0.71, and 0.024, respectively. Also, unlike mononuclear aromatics, palladium reduces substituted naphthalenes at substantially higher rates than does either platinum or rhodium. For example, the rate constants, k x 10 in mol sec" g catalyst", in acetic acid at 50 C and 1 atm, were (for 1,8-diisopropylnaphthalene) Pd (142), Pt(l8.4), and Rh(7.1)(25). 

Palladium may not be preferred for dihydric aromatics. Dihydroresorcinol was obtained in 87% yield by alkaline hydrogenation of resorcinol over 5% Rh-on-C (65) and in only 50-60% yield over Pd-on-C 15). A 77% yield of the dione was obtained by alkaline hydrogenation of 3,5-dihydroxyphenylacetic acid over a 10% loading of 5% Rh-on-AljOj at 55"C and 55 psig (39a). 

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