Palladium® acetate

The method is basically an application of the Wacker oxidation except that the catalyst used is palladium acetate ( Pd(AcO)2 or Pd(02CCH3)2). the solvent is acetic acid or tert-butyl alcohol and the oxygen source is the previously suggested hydrogen peroxide (H202)[17]. 

Benzyloxy-6-bromo-4-nitro-JV-(2-propeny])aniline (5.82 g, 16 mmol), tetra-ii-butylammonium bromide (5.16 g, 16 mmol) and titjN (4.05 g, 40 mmol) were dissolved in DMF (15 ml). Palladium acetate (72 mg, 2 mol%) was added and the reaction mixture was stirred for 24 h. The reaction mixture was diluted with EtOAc, filtered through Cclite, washed with water, 5"/o HCl and brine, dried and evaporated in vacuo. The residue was dissolved in CHjClj and filtered through silica to remove colloidal palladium. Evaporation of the eluate gave the product (4.32 g) in 96% yield. 

Several newer methods take advantage of the highly selective nature of organopaHadium reagents. A palladium acetate-triarylphosphine catalytic system has been employed to induce the coupling of bromobenzene with the desired acrylate ester (13). 

There are reports of an increasing number of palladium-assisted reactions, in some of which the palladium has a catalytic function. Thus furan and thiophene undergo facile palladium-assisted alkenylation giving 2-substituted products. Benzo[6 Jfuran and TV- acetyl-indole yield cyclization products, dibenzofurans and carbazoles respectively, in addition to alkenylated products (8UOC851). The arylation of pyrroles can be effected by treatment with palladium acetate and an arene (Scheme 86) (81CC254). 

In a related study, the precursor 41 could be amiulated either by irradiation or by treatment with palladium acetate in acetic acid to provide indolocarbazoles 42 and 43 in yields of 37% and 55%, respectively (Scheme 8). Both products were eventually deprotected efficiently to give 44 and transformed further under reductive conditions to staurosporinone 45, the aglycone of 8, Alternatively, a shorter route encompassing deprotection of 41, followed by cychzation by irradiation in the presence of iodine and subsequent reduction, gave 45 in an even better overall yield (98T6909). 

In a recent communication, the parent system 2 has been obtained in poor yields (16% and 10%, respectively) from the double cyclization of N-diphenyl-1,3-phenylenediamine either by using two equivalents of palladium acetate in refluxing acetic acid or by irradiation in methanol in the presence of a catalytic amount of iodine (00SC3651). All the available approaches sununarized so far were marred by harsh reactioi conditions or troublesome-to-prepare starting materials, leading to low overall yields of the desired products and difficulty in introducing sensitive substituents. 

Diphenylimidazole with palladium acetate forms the cyclometallated complex 80 (X = OAc) (97AOC491). The acetate group is replaced by chloride or bromide when 80 (X = OAc) reacts with sodium chloride or lithium bromide, respectively, to give 80 (X = C1, Br). Bromide with diethyl sulfide forms the mononuclear complex 81. Similar reactions are known for 1 -acetyl-2-phenylimidazole (96JOM(522)97). 1,5-Bis(A -methylimidazol-2-yl)pen-tane with palladium(II) acetate gives the cyclometallated complex 82 (OOJOM (607)194). 

Dimethyl-1,2,4-triazolium iodide with palladium acetate yields the carbene adduct 182 (97JOM(530)259). Under water it undergoes cis-trans isomerization to 183. Some other derivatives were reported in 1981 (81BCSJ800). 1,1 -Methylenebis(4-alkyl-l,2,4-triazolium)diiodides (alkyl = /-Pr, n-Bu, octyl) with palladium(II) acetate give the mononuclear complexes [L Pdl ] (99EJIC1965), where L2= l,l -methylenebis(4-R-l,2,4-triazol-2-ylidene) (R = /-Pr, n-Bu, octyl). Thermolysis of the products in THF gives the rran -dinuclear complexes 184... 

Bromination of the diphenyl indole derivative 316 with bromine in DMF or trimethylammonium bromide afforded the 7-bromo derivative 317. Reaction with allyl bromide or its derivatives gave A-allyl derivatives 318 that upon cyclization with palladium acetate gave 7,9-dimethoxy-l,2-diphenylpyrrolo[3,2,l-// ]quinoline derivatives 319 (92T7601) (Scheme 57). 

The parent TMM precursor (1), now commercially available, has played a pivotal role in the execution of many synthetic plans directed at natural and unnatural targets. Reaction of (1) with 2-(methoxycarbonyl)cyclohexenone (14, R=C02Me) in the presence of palladium acetate and triethyl phosphite produced the adduct (15) in near quantitative yield. This cycloadduct is a critical intermediate in the total synthesis of a hydroxykempenone (16), a component of the defensive substances secreted by termites (Scheme 2.5) [12]. In accord with a previous observation by Trost that unactivated 2-cyclohexenone reacts poorly with TMM-Pd [13], the substrate (14, R=Me) was essentially inert in the cycloaddition. 

Perhydroindans (46) and (47) could be obtained in 73% yield from the carbonate (48) with only minor amounts of elimination product. The use of BSA and the triisopropyl phosphite-palladium acetate catalytic system provides further improvement. The low cisitrans selectivity in the formation of the first ring, and rapid subsequent cyclization account for the fact that the ratio of (46) to (47) is only 2 1 (Scheme 2.14). Even the presence of a bulky trialkylsiloxyl substituent adjacent to the vinyl sulfone moiety has only a minor influence on the cisitrans selectivity [24]. 

There is significant metal-metal bonding in the platinum compound, whose geometry involves a square of platinum atoms another important difference is that the coordination geometry is square planar in palladium acetate but octahedral in the platinum analogue. Different oligomers exist in solution, broken down by adduct formation. Palladium(II) acetate may be obtained as brown crystals from the following reaction [65] ... 

The importance of palladium acetate lies in its ability to catalyse a wide range of organic syntheses functionalizing C-H bonds in alkanes and in aromatics, and in oxidizing alkenes. It has been used industrially in the... 

Figure 3.26 The structures of (a) palladium acetate and (b) platinum acetate. (Reproduced with permission from J. Chem. Soc., Chem. Commun., 1970, 659 and Acta Crystallogr. Sect. B, 1978,...

Tetrakis(tripheiiylphosphine)palladium(0) is often used for this reaction. However, Pd(II) complexes such as bis(triphenylphosphine)palladium dichloride or palladium acetate are also commonly employed for convenience, as they are stable in ah. The base is typically a secondary or tertiary amine such as triethy-lamine. Weak bases such as sodium (potassium) acetate, bicarbonate, or carbonate are also used. 

The Suzuki reaction has been successfully used to introduce new C - C bonds into 2-pyridones [75,83,84]. The use of microwave irradiation in transition-metal-catalyzed transformations is reported to decrease reaction times [52]. Still, there is, to our knowledge, only one example where a microwave-assisted Suzuki reaction has been performed on a quinolin-2(lH)-one or any other 2-pyridone containing heterocycle. Glasnov et al. described a Suzuki reaction of 4-chloro-quinolin-2(lff)-one with phenylboronic acid in presence of a palladium-catalyst under microwave irradiation (Scheme 13) [53]. After screening different conditions to improve the conversion and isolated yield of the desired aryl substituted quinolin-2( lff)-one 47, they found that a combination of palladium acetate and triphenylphosphine as catalyst (0.5 mol %), a 3 1 mixture of 1,2-dimethoxyethane (DME) and water as solvent, triethyl-amine as base, and irradiation for 30 min at 150 °C gave the best result. Crucial for the reaction was the temperature and the amount of water in the... 

Another difference between the two mechanisms is that the former involves 1,2 and the latter 1,3 shifts. The isomerization of 1-butene by rhodium(I) is an example of a reaction that takes place by the metal hydride mechanism, while an example of the TT-allyl complex mechanism is found in the Fe3(CO)i2 catalyzed isomerization of 3-ethyl-l-pentene. " A palladium acetate or palladium complex catalyst was used to convert alkynones RCOCSCCH2CH2R to 2,4-alkadien-l-ones RCOCH= CHCH = CHCHR. ... 

A methyl group can be introduced into an aromatic ring by treatment of diazonium salts with tetramethyltin and a palladium acetate catalyst." The reaction has been performed with Me, Cl, Br, and NO2 groups on the ring. A vinylic group can be introduced with CH2=CHSnBu3. 

Diazonium salts react with oximes to give aryl oximes, which are easily hydrolyzed to aldehydes (R = H) or ketones." A copper sulfate-sodium sulfite catalyst is essential. In most cases higher yields (40-60%) are obtained when the reaction is used for aldehydes than for ketones. In another method for achieving the conversion ArNj —> ArCOR, diazonium salts are treated with R4Sn and CO with palladium acetate as catalyst. In a different kind of reaction, silyl enol ethers of aryl ketones, Ar C(OSiMe3)=CHR, react with sohd diazonium fluoroborates, ArNj BF4, to give ketones, ArCHRCOAr. " This is, in effect, an arylation of the aryl ketone. 

Carboxylic acids can be prepared in moderate-to-high yields by treatment of diazonium fluoroborates with carbon monoxide and palladium acetate or copper(II) chloride. The mixed anhydride ArCOOCOMe is an intermediate that can be isolated. Other mixed anhydrides can be prepared by the use of other salts instead of sodium acetate." An arylpalladium compound is probably an intermediate." ... 

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