Palladium acetate applications

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]. 

Palladium acetate, [PdO —02CCH3)2l3, possesses a unique quality that makes it attractive for solid state decomposition studies as well as technological applications. It can be spin-coated from solution to form a homogeneous, apparently amorphous solid film. This provides large uniform areas over which we can study the effects of various irradiation sources on the chemical nature of the film. The bulky structure of palladium acetate, shown in Figure 1 (8), may offer a partial explanation of the molecule s ability to achieve an amorphous metastable phase upon rapid evaporation of solvent. 

An interestingly short total synthesis of quadrone was developed by Kende and coworkers who made application of Pd(II)-mediated cycloalkenylation of silyl enol ethers (Scheme LV) Their point of departure was 609 which was converted directly to 610, Reaction of this silyl enol ether with palladium acetate in acetonitrile gave predominantly 6JI which could be cyclized to 612. From this intermediate, it was possible to prepare the known keto acid. 

Another interesting application of microwave irradiation is found in the selective dehalogenation of the iodinated indole alkaloid Plakohypaphorine F, described by E. Fattorusso et al. [117,118] (Scheme 32). The bis-halogenated compound was treated with potassium formate and palladium acetate under controlled microwave irradiation, resulting in selective deiodination. The choice of the solvent, in this case DMSO, was found to be crucial. 

Applications of this reaction are not limited to advanced materials, but can be applied to natural product synthesis. Indeed, indoles have quite recently (in 2008) been arylated in the presence of palladium acetate and silver oxide (Scheme 10.52).84... 

In a finding of greater practical significance. Overman and coworicers showed that the reactions could be carried out with catalytic amounts of the palladium(II) complex, and that the catalytic effect was broadly applicable to acyclic 1,5-dienes as well7 In a typical example (equation 32), 2-methyl-3-phe-nyl-l,5-hexadiene rearranges in 1 h at room temperature in 87% yield in the presence of 0.06 equiv. of bis(benzonitrile)palladium dichloride, in contrast to the thermal rearrangement which has t n = 13 h at 177 °C. The cat yst thus provides an estimated rate acceleration of about 10 °. The product is a 93 7 mixture of ( )- and (Z)-isomers, corresponding to the equilibrium ratio. Palladium acetate and tetra-kis(triphenylphosphine) were ineffective as catalysts. One serious limitation is that the catalyzed reaction occurs only with those 1,5-dienes which possess an alkyl or aryl substituent at C-2 or C-5 (but not both). 

Commercially available palladium compounds in the presence of various ligands have often been used as catalysts (Table 3-1). The first choice is often the air-stable and relatively inexpensive palladium acetate however, several of the other published variants can be preferable in certain applications. It is commonly assumed that the palladium(II) species is reduced in situ by the solvent, the alkene [11], the amine [12] or the added ligand (frequently a phosphane, which is oxidized to a phosphane oxide) [13]. In some cases, highly dispersed elemental palladium on charcoal can be applied. In the case of alkenyl or aryl bromides, phosphanes are necessary to avoid precipitation of palladium black (c.f., however. Section 3.2.4.), whereas iodides have been reported to be less reactive in the presence of phosphanes. Triflates have been found to be more reactive in the presence of chloride ions, as the chloride ligand is more easily removed from palladium than the tiiflate ion [14], However, this also has become questionable, because successful coupling reactions of alkenyl triflates have been performed in the absence of chloride ions [15]. 

An interesting application of the Fujiwara-Moritani/oxidative Heck reaction for the synthesis of benzo furans was recently reported by the Stoltz lab [31]. A variety of allyl phenyl ethers (all containing electron-rich aryl components) react with 10 mol% palladium acetate, 20 mol% ethyl nicotinate, 20 mol% sodium acetate, and one equivalent of benzoquinone at 100°C to provide benzofurans in 52-79% yield (e.g. 16—>17). The mechanism of this transformation begins with arene palladation of Pd(II) followed by olefin insertion, p-hydrogen elimination, and olefin isomerization to the thermodynamically favored benzofuran product. The resulting Pd(0) species is then oxidized to Pd(ll) thus regenerating the active catalyst. 

O/t/20-arylation of benzoic acids is often preferable to ortho-arylation of benzamides if conversion of the amide moiety to other functional groups is desired. However, only a few reports have dealt with the orf/io-functionalization of free benzoic acids due to challenges that involve such transformations. The reactions can be complicated by decarboxylation of the product and the starting material. Despite those difficulties, several methods for direct o/t/io-arylation of benzoic acids have been developed. Yu has shown that arylboronates are effective in arylation of benzoic acids under palladium catalysis [59], The reactions require the presence of palladium acetate catalyst, silver carbonate oxidant, and benzoquinone. Even more interestingly, the procedure is applicable to the arylation of unactivated sp3 C-H bonds in tertiary carboxylic acids such as pivalic acid (Scheme 13) if aryl iodide coupling partner is used. Aryl trifluoroborates can also be used [60],... 

With this bicyclic intermediate available in sizeable amounts, ready advance to 111 could be conveniently accomplished prior to annulation of the second five-membered ring (Scheme XIV). 1,3-Carbonyl transposition was realized by complete eradication of the original carbonyl by Ireland s method [60] followed by allylic oxidation. Application of the Piers cyclopentannulation protocol [61] to 111 made 113 conveniently available. Introduction of a methyl group into ring B was brought about by treatment of the kinetically derived enol triflate [62] with lithium dimethylcuprate [63], Hydrolysis of 114 gave the dienone, which was directly transformed into 115 by oxidation of its silyl enol ether with palladium acetate in acetonitrile [64],... 

Reaction of organic halides with alkenes catalyzed by palladium compounds (Heck type reaction) is known to be a useful method for carbon-carbon bond formation at unsubstituted vinylic positions. The first reports of the application of MW methodology to this type of reaction were published by Hallberg et al. in 1996 [109] and by Diaz-Ortiz et al. in 1997 [llOj both used in triethylamine solutions. Later, Ville-min et al. studied the possibility of Heck coupling of iodoarenes with methyl acrylate in aqueous solution under pressurized conditions [111]. The reactions were conducted in a Teflon autoclave under the action of MW irradiation in the presence of palladium acetate, different phosphine ligands, and tetrabutylammonium hydrogen sulfate (TBAHS) as PTC catalyst, to afford the desired coupling products in 40 to 90% yield. 

One of the traditional methods for applications of the aliphatic Claisen rearrangement has used Mercuric salts to prepare vinyl ether as illustrated in the use of the allylic alcohol (28) en route to aldehyde 29. The chemical development group at Boehringer-Ingelheim has developd a mild palladium acetate-phenanthroline catalyst 31 for the sequential allyl vinyl ether-Claisen process utilizing commercially available triethyleneglycol divinyl ether which avoids the use of mercuric acetate. ... 

Apart from routine applications to cyclopropane synthesis,the application of new catalysts to the decomposition of diazo-compounds has received considerable attention. The use of palladium acetate, originally reported in 1972 by Paulissen et o/., has been extended and applied to diazomethane and ethyl diazoacetate in the presence of aP-unsaturated carbonyl compounds. With a- and a-substituted aP-unsaturated ketones, stereospecific cis-addition occurs in excellent yields, but the catalyst proves to be ineffective with analogous trisubstituted olefins, as illustrated for the formation of (110) with diazomethane. The use of palladium chloride with the... 

In 2000, Nolan and Lee reported the successful application of NHC ligands in this particular arylation reaction [101]. By combining palladium acetate and the imidazolium salt IPr-HCl (IPr = l,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene), it was possible to react phenyltrimethoxysUane (as well as vinyltrimethoxysilane) with a variety of aryl bromides and aryl chlorides, including 2-bromopyridine giving the arylated product in high yields (Scheme 1.36) (see Experimental Procedure below). 

Xu, Z., Wang, Q., Zhu, J. (2013). Palladium-catalyzed decarboxylative vinylation of potassium nitrophenyl acetate application to the total synthesis of (—)-goniomitine. Angewandte Chemie International Edition, 46, 3272-3276. 

Direct metallation of aromates can be conveniently performed with palladium acetate. The reaction is also of application with heterocycles [57] (example 2) ... 

Figure 5 gives the results obtained in the following reaction conditions starch 12g, butadiene ca 40g, catalyst Pd(OAc)2/TPPTS 1/3, aqueous NaOH (O.IM) 50ml/iPrOH 10ml, 3h. At 90°C, with 0.5 wt.% of Pd(OAc)2, the DS reached almost 0.6 while less than 0.3 was achieved with 0.12 wt% catalyst. At 50°C, the DS was lower but much less affected by the catalyst/starch ratio, thus the DS decreased from 0.15 to 0.08 as the amount of catalyst decreased from 0.5% to 0.05%. This is because at 90°C Pd/TPPTS complex is unstable and decomposes progressively into palladium metal whereas at 50°C the catalyst is stable enough. When the reaction was performed in the presence of 0.25% palladium acetate, 0.08 wt% residual palladium was detected by chemical analysis of modified starch after reaction at 50°C. In contrast, no palladium was detected in the modified polymer when the reaction was conducted in the presence of 0.05% palladium. An optimum DS of 0.06 suitable for application in latex preparation for decorative paints was obtained with 0.03% palladium at 50X. 

Applications of these C-H activation processes in polymerization reactions have also been reported in the literature. For example, a palladium-catalyzed C-H arylation polycondensation was carried out between a thiophene unsubstituted at the 2- and 5- positions and its 2,5-dibromo derivative. The transformation was effected in the presence of palladium acetate, a phosphine, and cesium carbonate in DMF at 100 °C for 48 h (eq 23). A survey of different phosphines showed that similar yields, molecular weights (Mn), and polydispersity indexes (PDI) could be obtained using di-tert-butyl(methyl)phosphonium tetrafluoroborate or tri-cyclohexylphosphonium tetrafluoroborate as the ligand. ... 

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... 

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