Heck coupling palladium® acetate

The Heck coupling reaction appeared to be a route of choice to achieve the synthesis of the modified-DIOP ligands. We previously studied the palladium-catalyzed coupling of acrolein and acrolein acetals with several polyaromatic and heteroaromatic bromides either in the presence of homogeneous or heterogeneous catalytic systems (6, 7). After optimization of the reaction conditions, high conversions and selectivities were achieved except with anthracenyl derivatives (8). Based on these results, we developed the synthesis of the desired ligands. The... 

A very recent addition to the already powerful spectrum of microwave Heck chemistry has been the development of a general procedure for carrying out oxidative Heck couplings, that is, the palladium)11)-catalyzed carbon-carbon coupling of arylboronic acids with alkenes using copper(II) acetate as a reoxidant [25], In a 2003 publication (Scheme 6.6), Larhed and coworkers utilized lithium acetate as a base and the polar and aprotic N,N-dimethylformamide as solvent. The coupling... 

An attempt to functionalize position 6 of the oxazolo[4,5- ]pyridine 112 was unsuccessful when using -butyllithium and an electrophile at —78°C however, successful Heck coupling was achieved using palladium(ll) acetate and tri-o-tolylphosphine in dimethylformamide (DMF) with triethylamine as base (Equation 20 Table 19) <1996TL2409, 1997T5159, 1998BMC1963>. The Stille (Equation 21 Table 20) and Suzuki couplings were also found to be successful (Equation 22). 

The reaction of /V-pentenyl-2-iodoindole in the presence of a palladium-triphenylphosphine catalyst led to the formation of a mixture of isomeric products in good yield (4.8.), Addition of thallium(I) acetate favoured the formation of an exocyclic double bond, while in its absence the product containing the endocyclic olefin moiety is formed preferentially. The shortening of the A-alkenyl chain by one carbon leads to the selective formation of a five membered ring.9 Starting from indole-carboxamide derivatives both /3-. and carbolinones are available in intramolecular Heck coupling. 

The Heck coupling is also efficient in the formation of pyrane derivatives. By starting from the appropriately substituted 1,3,5-tribromobenzene derivative, three fused pyrane rings were constructed in the same reaction. The triple Heck reaction in the presence of palladium acetate and triphenylphosphine led to the formation of the tetracyclic product in good yield accompanied by a minor amount of the tricyclic intermediate(4.12.).13... 

The Heck reactions depicted so far all involve the coupling of halopyridines and other olefins. The alternate approach, coupling of a vinylpyridine with an aryl halide is also feasible, although less commonly employed. 4-Vinylpyridine was coupled successfully with diethyl 4-bromobenzylphosphonate (7.50.) in the presence of a highly active catalyst system consisting of palladium acetate and tn-o-tolylphosphine to give the desired product in 89% yield, which was used for grafting the pyridine moiety onto metal oxides.70... 

A polyethylene glycol-polystyrene graft copolymer palladium catalyst has been used in allylic substitution reactions of allyl acetates with various nucleophiles in aqueous media.58 Another polymer-bound palladium catalyst 40 was developed and used in a Heck coupling of allylic alcohols with hypervalent iodonium salts to afford the substituted allylic alcohols as the sole products under mild conditions with high catalytic efficiency.59 The same polymer-bound palladium catalyst has also been used for Suzuki cross-coupling reactions.60... 

A nonclassical substrate for the Heck reaction is 2,3-epoxycyclohexanone. The reactivity of this molecule under Heck coupling conditions is most likely attributed to its in situ isomerization to 1,2-cyclohexanedione. The 1,2-diketone subsequently reacts with aryl bromides as an olefin via the enol tautomer. Thus, within 5 to 30 min of directed microwave heating of the aqueous PEG mixture, up to 13 different C3-arylations were conducted using less than 0.05 mol % palladium acetate and no phosphine ligand (Scheme 12) [51]. 

The useful and selective reactivity of arylboronic acids makes them favorite building blocks for many modern organic chemistry applications. Arylboronic acids also serve as highly useful arylpalladium precursors in palladium(II)-catalyzed oxidative Heck reactions. Andappan et al. developed a microwave-accelerated protocol for oxidative Heck couplings using cop-per(II) acetate as the palladium reoxidant [52]. The method proved to be... 

Over 35 years ago, Richard F. Heck found that olefins can insert into the metal-carbon bond of arylpalladium species generated from organomercury compounds [1], The carbopalladation of olefins, stoichiometric at first, was made catalytic by Tsutomu Mizoroki, who coupled aryl iodides with ethylene under high pressure, in the presence of palladium chloride and sodium carbonate to neutralize the hydroiodic acid formed (Scheme 1) [2], Shortly thereafter, Heck disclosed a more general and practical procedure for this transformation, using palladium acetate as the catalyst and tri-w-butyl amine as the base [3], After investigations on stoichiometric reactions by Fitton et al. [4], it was also Heck who introduced palladium phosphine complexes as catalysts, enabling the decisive extension of the ole-fination reaction to inexpensive aryl bromides [5],... 

The stilbazoles have been synthesized using three different routes, and these are now described briefly (Figs. 2 and 3). The first attempts involved reacting 4-alkoxybenzaldehyde with 4-picoline in acetic anhydride, which led to extremely poor yields of the stilbazoles after a week s work (2). This route was subsequently superseded by a Heck coupling method in which 4-vinylpyridine was reacted with 4-alkoxyiodobenzene in the presence of a palladium catalyst (2). The reaction worked very... 

It was shown that palladacycles 1, prepared from palladium(II) acetate and the tris(a-tolyl)- or trimesitylphosphane, are excellent catalysts for the Heck coupling of triflates and halides (including certain aryl chlorides). In this case, oxidation states -l-U and +IV appear to be involved in the catalytic cycle [16]. 

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. 

More recently, Najera et al. performed a number of Heck reactions of deactivated aryl halides and styrenes under phosphane-free conditions using oxime-derived palladacycles or palladium acetate as catalyst [113], Coupling can be performed either vith chcyclohexylmethylamine as base and TBAB as PTC catalyst or in neat vater vith triethylamine in N,N-dimethylacetamide (DMA) solutions under the action of MW irradiation. 

A series of Pd-catalyzed intramolecular Heck reactions of N-(2-halophenyl)-substituted enaminones was performed by Pombo-Villar et al. [114]. The reactions were performed in the presence of palladium acetate with a phosphonium ligand as catalyst, sodium acetate, and tetrabutylammonium chloride (TBACl) as the PTC catalyst in DMF solution to afford desired coupling product in 25 to 99% yields (Eq. 79). 

Utilizing this principle, Heck reactions were performed [57]. The silica gel was derivatized with a CgHiy-trimethoxysilane to obtain the desired reversed phase properties, followed by treatment with palladium acetate and triph-enylphosphine in cyclohexane. After removal of the solvent, an air-stable catalyst supported on reversed-phase silica gel (RPSG) was formed. This supported catalyst was employed with variable success in Heck C-C coupling reactions, as depicted in Scheme 16. 

The Heck coupling is an example of another key metal-catalyzed transformation. Again, this has been incorporated into the undergraduate laboratory curriculum in conjunction with the use of microwave heating (Scheme 6.20). Similar conditions to those developed for the Suzuki reaction were used with either palladium acetate (0.4 mol%) or palladium chloride (ICP standard, 0.004 mol%) as catalyst. 

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