And carbonylation of aryl

Subsequent studies on the reactivities of neutral and cationic alkyl- and aryl- palladium complexes revealed that the creation of a vacant site adjacent to the alkyl or aryl ligand causes marked enhancement in reactivity toward j8-hydrogen migration. The implications of these results on the fundamental processes of the transition metal alkyls and aryls with the mechanisms of Pd-catalyzed organic synthesis, such as arylation of olefins and carbonylation of aryl halides, have been discussed. 

Pd(II) salts promote the carbonylation of organomercury compounds. Reaction of phenylmercury chloride and PdCh under CO pressure affords benzophenone (429)[387]. Both esters and ketones are obtained by the carbonylation of furylmercury(Il) chloride in alcohol[388]. Although the yields are not satisfactory, esters are obtained by the carbonylation of aryl- and alkylmercuryfll) chlorides[389,390]. One-pot catalytic carbonylation of thiophene, furan, and pyrrole (430) takes place at the 2-position via mercuration and transmetallation by the use of PdCb, Hg(N03), and CuCl2[391]. 

Formation of carboxylic acids ami their derivatives. Aryl and alkenyl halides undergo Pd-catalyzed carbonylation under mild conditions, offering useful synthetic methods for carbonyl compounds. The facile CO insertion into aryl- or alkenylpalladium complexes, followed by the nucleophilic attack of alcohol or water affords esters or carboxylic acids. Aromatic and a,/ -unsaturated carboxylic acids or esters are prepared by the carbonylation of aryl and alkenyl halides in water or alcohols[30l-305]. 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Aldehydes can also be prepared by the carbonylation of aryl and alkenyl halides and triflate, and benzyl and allyl chlorides using tin hydride as a hydride source and Pd(PhjP)4 as a catalyst[377]. Hydrosilancs arc used as another hydride source[378]. The arenediazonium tetralluoroborate 515 is converted into a benzaldehyde derivative rapidly in a good yield by using Et ,SiH or PH MS as the hydride source[379]. 

The carbonylation of aryl iodides in the presence of alkyl iodides and Zn Cu couple affords aryl alkyl ketones via the formation of alkylzinc species from alkyl iodides followed by transmetallation and reductive elimination[380]. The Pd-catalyzed carbonylation of the diaryliodonium salts 516 under mild conditions in the presence of Zn affords ketones 517 via phenylzinc. The a-diketone 518 is formed as a byproduct[381],... 

The aryl- and heteroarylfluorosilanes 541 can be used for the preparation of the unsymmetrical ketones 542[400], Carbonylation of aryl triflate with the siloxycyclopropane 543 affords the 7-keto ester 545. In this reaction, transme-tallation of the siloxycyclopropane 543 with acylpalladium and ring opening generate Pd homoenolate as an intermediate 544 without undergoing elimination of/3-hydrogen[401],... 

Isoxazolines with alkyl substituents are also all liquids (or low melting solids) and incorporation of aryl substituents results in crystallinity. Introduction of carboxy substituents and endocyclic carbonyl or imino groups also has the anticipated effect, with crystalline products being isolated. These trends are illustrated by the data compiled in Table 2. 

M-NHC catalysts in this area. Metal catalysed carbonylation also provides an alternative synthetic ronte to the prodnction of materials that traditionally reqnire highly toxic precnrsors, like phosgene. This section discnsses carbonylation of aryl hahdes, oxidative carbonylation of phenolic and amino componnds, carbonylation of aryl diazoninm ions, alcohol carbonylation, carbonylative amidation, and copolymerisation of ethylene and CO. 

A number of Pd or Cu catalysts bearing NHC ligands have been prepared for carbonylation of aryl halides. Nacci and co-workers synthesised the benzothiazole carbene ligated Pd complex 32 (Fig. 9.6) and tested it for aryl halide carbonylation... 

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... 

Scheme 5. Palladium-catalyzed carbonylations of aryl halides and pseudohalides...

CARBONYLATION OF ARYL AND VINYL HALIDES LEADING TO CARBOXYLIC ACIDS AND RELATED COMPOUNDS... 

In a slightly less convenient procedure, but one which has general versatility, carbonylation of aryl (or vinyl) palladium compounds produces aryl, heteroaryl, and vinyl carboxylic acids. As with the other procedures, immediate upon its formation, the carboxylate anion migrates to the aqueous phase. Consequently, haloaromatic acids can be obtained from dihaloarenes, without further reaction of the second halogen atom, e.g. 1,4-dibromobenzene has been carbonylated (90% conversion) to yield 4-bromobenzoic acid with a selectivity for the monocarbonylation product of 95%. Additionally, the process is economically attractive, as the organic phase containing the catalyst can be cycled with virtually no loss of activity and ca. 4000 moles of acid can be produced for each mole of the palladium complex used [4],... 

For the preparation of a-ketoamides, palladium-catalyzed double carbonylation of aryl halides with carbon monoxide and secondary amines is also a useful reaction Kobayashi, T. Tanaka, M. J. Organomet. Chem. 1982, 233, C64 Ozawa, F. Soyama, H. Yamamoto, T. Yamamoto, A. Tetrahedron Lett. 1982, 23, 3383. 

Very high regioselectivities (> 99.5% iso) were obtained, using PdCl2(PhCN)2 in combination with (+)-neomethyldiphenylphosphine and toluene-j9-sulfonic acid, under mild conditions (70 °C and 10 bar). More recently, the palladium-catalyzed alkoxycarbonylation and amido-carbonylation of aryl bromides and iodides in [bmim][BF4] and [bmim][PF6] has been described. Enhanced reaction rates were observed compared to conventional media and the ionic liquid-catalyst could be recycled. 

The carbonylation of o-diiodobenzene with a primary amine affords the phthalimide 501 [355,356], Carbonylation of iodobenzene in the presence of odiaminobenzene (502) and DBU or 2,6-lutidine affords 2-phenylbenzimida-zole (503)[357], The carbonylation of aryl iodides in the presence of pentafluor-oaniline affords 2-arylbenzoxazoles directly. 2-Arylbenzoxazole is prepared indirectly by the carbonylation of n-aminophenol[358]. The optically active aryl or alkenyl oxazolinc 505 is prepared by the carbonylation of the aryl or enol triflates in the presence of the opticaly active amino alcohol 504, followed by treatment with thionyl chloride[359]. 

Formation of aldehydes. Aldehydes can be prepared by the carbonylation of halides in the presence of various hydride sources. The carbonylation of aryl and alkenyl iodides and bromides with CO and H (1 1) in aprotic solvents in the presence of tertiary amines affords aldehydes[373,374]. Aryl chlorides, as tricarbonylchromium derivatives, are converted into aldehydes at 130 C[366], Sodium formate can be used as a hydride source to afford aldehydes. Chlorobenzene (514) was carbonylated at 150 °C to give benzaldehyde with CO and sodium formate by using dippp as a ligand[375,376]. 

The concept of CPTC has been applied in a large number of catalytic reactions such as reduction of allyl chlorides with HCOONa, carbonylation of aryl and allyl halides, allylation of aldehydes, cyanation of aryl halides etc.214 For example, Okano et a/.215 reduced l-chloro-2-nonene to afford 1-nonene and... 

Acetylenic ketones.3 PdCl2(dppf) is generally the most satisractory catalyst for synthesis of acetylenic ketones by carbonylation of aryl and vinyl halides in the presence of a terminal acetylene. 

Co(OAc)2 in the presence of sodium hydride and a sodium alkoxide has been used to catalyze the carbonylation of aryl bromides, giving mixtures of carboxylic acids and esters, again at normal pressure. When amines were present, amides were formed. Unfortunately, nothing is known about the nature of the cobalt complexes involved. 

Methyl ketones can be prepared by the carbonylation of aryl, benzyl and thienyl bromides and iodides in the presence of tetramethyltin (equation 102). This reaction also requires raised temperature and pressure. [Ni(CO)2(PPh3)2] (101) was used as catalyst.473... 

Heck and co-workers have reported the catalytic carbonylation of aryl and vinyl bromides and iodides and of benzyl chlorides in the presence of alcohols to give esters.479 The general reaction is summarized in equation (107) in which RX represents the above organic halides. 

Unsymmetricatl ketones can be obtained by the palladium-catalyzed carbonylation of aryl, alkyl and vinyl bromides and iodides in the presence of tetraalkyl- or tetraaryl-tin compounds (equation 113).489,490 The catalyst precursors used were complexes (102), (107) and [PdCI2(AsPh3)2]. 

Ikariya and co-workers reported an efficient palladium-catalyzed carbonylation of aryl halides in sc C02 (eq. 2.10) (Kayaki et al., 1999). 2-Iodobenzyl alcohol was converted to the phthalide in the presence of PdCl2L2 [L = PMe3, PPh3, MeCN, P(OEt)3, P(OPh)3, PPh(OMe)2, PPh2(OMe)] with higher rates in sc C02 than in toluene. 

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