Aryl palladium-catalyzed 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...

Bromophenyl)ethanol undergoes a palladium-catalyzed carbonylation which results in the formation of isochroman-l-one (79H(12)92l). It is considered that the reaction involves formation of an aryl-palladium complex (624) through insertion of the zerovalent palladium complex (623) into the aryl halide. Insertion of carbon monoxide followed by reductive elimination of the metal as a complex species leads to the isochromanone (Scheme 242). 

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. 

Palladium-catalyzed carbonylation reactions with aryl halides are powerful methods of generating aromatic amides, hydrazides, esters and carboxylic acids [25]. We have previously reported the exploitation of Mo(CO)6 as a robust carbon monoxide-releasing reagent in palladium-catalyzed carbonylation reactions [26-29]. This stable and inexpensive solid delivers a fixed amount of carbon monoxide upon heating or by the addition of a competing molybdenum coordinating ligand (for example DBU). This allows for direct liberation of carbon monoxide in the reaction mixture without the need for external devices. 

Iodophenyl acetates undergo palladium-catalyzed carbonylation in the presence of aryl alkynes to yield flavones (Equation 309) <20000L1765>. 2-Iodophenols can similarly undergo a palladium-catalyzed carbonylation in the presence of terminal alkynes to afford chromones (Equation 310) <2005JOC6097>. 

In 1979 the reaction of benzyl and aryl halides was reported with mechanistic discussions [8, 9]. The first palladium-catalyzed carbonylative coupling of organic halides with organotin compounds was reported by Tanaka in the same year (Scheme 4) [10,11]. 

Ma W, Li X, Yang J, Liu Z, Chen B, Pan X (2006) A convenient synthesis of aryl ferrocenylethynyl ketones and 2-ferrocenyl-4H-chromen-4-ones via palladium-catalyzed carbonylation coupling. Synthesis 2489-2492... 

The insertion of CO into palladium carbon bonds is a common step in many palladium-catalyzed carbonylation reactions and polymerizations. This reaction takes place under moderate CO pressure (1-3 atm). From the range of compounds that can be carbonylated, it can be inferred that CO will insert into alkyl, aryl, and alkynic bonds (equation 13). One of the few types of Pd-C bonds inert to CO insertion is the Pd-acyl bond, thus only single carbonylations are normally observed. However, a few examples of double carbonylation have been reported. In the case of palladium-catalyzed formation of PhCOCONEt2 from Phi, CO, and NHEt2, reductive elimination from a bisacyl complex has been established as the mechanism, rather than CO insertion into a Pd-acyl bond. 

Echavarren, A. M., Stille, J. K. Palladium-catalyzed carbonylative coupling of aryl triflates with organostannanes. J. Am. Chem. Soc. 1988, 110, 1557-1565. 

Alfhough direct nucleophilic addition is limited because of the low nucleophilicity of fhe fluoride ion, a palladium-catalyzed reaction enables the weak nucleophile to participate fhe addition reaction. In the presence of cesium fluoride, palladium-catalyzed carbonylation of an aryl halide gives fhe acyl fluoride in good yield (Scheme 2.5) [8]. 

The palladium-catalyzed carbonylation of organic halides is a convenient means of synthesizing carbonyl compounds. For example, the single carbonylation of aryl iodides has been applied to synthesize lactones and lactams (eq (69) and (70)) [97,98],... 

Palladium-catalyzed carbonylation of aryl triflates in the presence of an alcohol141 or amine1423 provides a good method for preparation of arenecarboxylic esters and amides from phenols (equation 121). However, palladium-catalyzed cyanation of 5,6,7,8-tetrahydro-2-naphthyl triflate with potassium cyanide failed completely whereas the more reactive tetrakis(triphenylphosphine)nickel(0) could catalyze the same reaction which gives the nitrile in a good yield142b (equation 122). 

The palladium-catalyzed carbonylation reaction with aryl halides is a powerful method for generating aromatic amides, hydrazides, esters, and carboxylic acids... 

Heck carbonylation involving the oxidative addition of aryl halides is not applicable to aliphatic halides, since alkyl halides react directly with nucleophiles. Tsuji developed a process of carbonylating allyl carbonates to form carboxylic esters by palladium-catalyzed carbonylation that is applicable to aliphatic substrates [60]. The process probably involves (a) the oxidative addition of allyl carbonates to Pd(0) species to form r/ -allyl palladium species, (b) CO insertion into the allyl-Pd bond to give acylpalladium species, (c) decarboxylation of the carbonate ligand to give alkoxide, and (d) liberation of butenoate esters by combination with the alkoxides as shown in Scheme 1.21. 

In palladium-catalyzed carbonylations, aryl triflates are used regularly as substrates [145-151], while arene diazonium salts [152-156] and diaryl iodonium salts [157-162] are less commonly applied. 

Tanaka and his associates demonstrated for the first time how to use non-volatile ionic liquids (ILs) as solvents in palladium-catalyzed carbonylations [163], In the case of alkoxycarbonylation of bromobenzene, higher yields were obtained when 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] was used as the reaction medium compared with standard conditions. And the selectivity for the monocarb-onylation of iodobenzene with t -PrOH or Et2NH was significantly enhanced by [bmim][BF4]. After separation of the products, the solvent-catalyst system was easily recycled and exhibited catalytic activity up to seven times. Since then the replacement of traditional solvents with quaternary ammonium halides, imidazoli-um- or pyridinium-derived ILs has gained increasing importance [164—173]. Recently, the phosphonium salt IL trihexyl(tetradecyl)phosphonium bromide has proven to be an effective reaction medium for various carbonylation reactions of aryl and vinyl bromides or iodides under mild conditions (Scheme 2.17) [174]. 

Larhed and colleagues developed the use of microwave irradiation in palladium-catalyzed carbonylations of aryl-X compounds [175-186]. Typically, these reactions were conducted in sealed vessels using microwave irradiation and either Mo(CO)g or formic acid derivatives as CO sources. Alternatively, alkoxy- and hydroxycarbonylations of aryl iodides with gaseous carbon monoxide have been performed by using pre-pressurized reaction vessels in conjunction with microwave heating [187-189]. 

Meyers and colleagues described the palladium-catalyzed carbonylative synthesis of oxazolines as early as 1992 [268]. Aryl or enol triflates made from the corresponding ketones and phenols, and also aryl halides, were used as starting materials and coupled with amino alcohols to give chiral a,)S-unsaturated or aryl oxazolines in good yields. Later on, Perry s group performed systematic studies on this one-pot, two-step process for the preparation of oxazolines (Scheme 2.37) [269, 270]. 

In 2007, BeUer and his colleagues developed the first general palladium-catalyzed carbonylation of aryl triflates with synthesis gas [39]. In contrast to aryl bromides, only the bidentate ligands dppe and dppp led to significant conversion... 

In 1993 Suzuki and colleagues described the palladium-catalyzed carbonylative coupling of aryl iodides with aryl boronic acids [13]. Various diarylketones were produced in high yields (Scheme 4.4). The choice of base and solvent was essential to obtain the desired ketones without biaryl by-products. The coupling of benzyl bromide was also described. In 1998 the group extended this methodology to aryl bromides and triflates [14]. In the case of aryl bromides, Nal or KI was required as an additive. The in situ transformation of aryl bromides to aryl iodides may be involved. 

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