Palladium, tetrakis catalyst

Because the Sonogashira coupling process outlined in Scheme 18 is initiated by the in situ reduction of palladium(n) to palladium(o), it would be expected that palladium(o) catalysts could be utilized directly. Indeed, a catalytic amount of tetrakis(triphenylphosphine)-... 

Palladium acetate and triphenylphosphine generate the active tri- or tetrakis(triphenylphosphine)palladium(0) catalyst on addition of sodium dimethyl malonate. 

Thus, for our present purposes a similar approach was followed using Suzuki cross-coupling reactions as the key steps in the synthesis of our target compounds. Symmetrically substituted compounds were synthesized in a twofold Suzuki crosscoupling reaction from commercially available p-substituted phenylboronic acids or esters and 4,4 -dibromobiphenyl or 4,4 -biphenyl-bis-boronic acid ester and a p-substituted arylhalide, respectively, using tetrakis (triphenylphosphino) palladium as catalyst together with cesium fluoride as base in dry tetrahydrofurane as shown in Scheme 8.1. The desired products were obtained in respectable yields after heating at reflux for 50 h. 

Further investigations including 109Ag NMR confirmed the in situ formation of alkynyl silver through jt complexation and proton abstraction.117 They also revealed that the best palladium catalyst, namely, palladium tetrakis(triphenylphosphine), played a key role, in that a phosphine liberated by decoordination ended up on the alkynyl silver, stabilizing it and rendering it more soluble.118 The resulting alkynyl silver then entered the palladium catalytic cycle at the transmetallation step (See section 10.6.2).105... 

When 3,3-dimethylcyclopropene is exposed to carbon monoxide under pressure in the presence of tetrakis(triphenylphosphane)palladium as catalyst, 3,3,6,6,10,10-hexamethyl-exo,enrfo-tet-racyclo[7.1.0.0 " .0 ]decan-8-one (hexamethyl-tris-cr-homotropone, 10) is formed as the main product (72.2%) along with carbonyl-free di- and oligomerization products. At ambient pressure with an in situ generated palladium(O) catalyst, only a 20% yield of the tetracyclic ketone 10 is obtained. 

Other catalysts, for example palladium acetate or palladium tetrakis(triphenylphosphane), have proved to be ineffective under these conditions122 777. 

Interestingly, the intramolecular variant of this transformation works best with palladium tetrakis as the catalyst.93,13 A combination of NaOf-Bu and K2CO3 serves as the base, although Et3N as solvent may also be used. 

Extending the intermolecular coupling, dihydroindoles (Scheme 4), dihydroquinolines, and other N-heterocycles were successfully synthesized by simple intramolecular trapping reactions, starting from alkylamino substituted aryl bromides. [8] Intramolecular amination can be achieved in the presence of tetrakis(triphenylphosphine)palladium as catalyst and stoichiometric amounts of base in toluene. Here, best results are obtained with mixtures of NaOtBu and potassium carbonate. 

Esters 106 (R = Me, Et or Pr = Et, Pr, r-Bu or PhCHi) of aliphatic carboxylic acids react with lithium acetylides 107 (R = H, C5 Hi i or Ph) in the presence of boron trifluoride etherate in THE to give acetylenic ketones 108 (equation 18). Palladium-[tetrakis(triphenylphosphine)]-copper(I) iodide catalyses the oxidative addition-decarboxylation of propargyl methyl carbonates, e.g. 109, with terminal alkynes to yield 1,2-dien-4-ynes (allenylacetylenes) 110. The regiochemistry of the palladium-catalyzed addition of phenylacetylene to the allenic ester 111 depends on the nature of the catalyst used palladium(III) acetate-triphenylphosphine yields a 81 19 mixture of adducts 112 and 113, while in the presence of tetrakis(carbomethoxy)palladacyclopentadiene-tris(2,4,6-trimethoxyphenyl)phosphine the ratio is reversed to 9 91 k... 

Palladium(0)-catalysts, in particular, tetrakis(triphenyl-phosphine)palladium have been found to catalyze 3-aza-Cope... 

Ruiz et al. [39] synthesized a series of l,4-bis(2-thienyl)-2,5-disubstituted benzene monomers with long-chain substituents at the 1- and 4-positions of the benzene ring by reacting the disubstituted benzene with bromine to provide reactive sites at the 2- and 5-positions for coupling with 2-thienyl zinc chloride in the presence of palladium tetrakis (triphenylphosphine) as catalyst at 50°C. In addition, they characterized the monomers using FT-IR, IH NMR, 13C NMR and elemental analysis. 

With the trimer 20 in hand, we could then address the final coupling reaction. Treatment of the core 9 with excess 2 0 in the presence of tetrakis(triphenylphosphine)palladium(0) catalyst afforded the target orthogonal system 21 that is approximately 25 A from end to end, one half of the length necessary to fulfill the initial Aviram model. 

As organosulfur compounds have been widely believed to be catalyst poisons, examples of the transition metal catalyzed reaction of these sulfur compounds have been limited. After the development of transition metal catalyzed addition of organosulfur compounds such as disulfides and thiols to carbon-triple bonds [9], many types of transition metal catalyzed addition reactions of organosulfur compounds have been developed. As to allenes, for example, the addition of thiols to terminal allenes successfully proceeds regioselectively at the internal double bonds of the allenes by the action of palladium acetate catalyst [10a,10b], while the disulfide addition to terminal allenes takes place at the terminal double bond in the presence of tetrakis (triphenylphosphine) palladium catalyst (Scheme 11.6) [10c]. 

Polycondensation and deprotection. The polycondensations of dibromides 3b and 4b with diboronic acid 5 were done according to standard procedures using 1.0 mol % of palladium tetrakis(triphenylphosphin) as catalyst precursor (10) (Figure 2). 

Kamiya I, Kawakami J, Yano S, Nomoto A, Ogawa A. A highly regioselective cyanothiolation of alkynes via oxidative addition of thiocyanates to tetrakis(triphenylphosphine) palladium(O) catalyst. Organometallics 2006 25 3562-4564. 

A variety of catalysts, solvents and amines as base can be employed for the Sonogashira reaction. Typical conditions are, e.g. tetrakis(triphenylphosphine)palladium(0)... 

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