Heck coupling carbonization

Finally, some recently published Heck couplings of aryl iodides, including the use of Pd(0) nanoparticles formed in situ [92] and heterogeneous Pd on carbon [93] should be mentioned here. 

Another methodology that is widely used for C-C bond formation is the Heck coupling (Heck, 1985 T.suji, 1995). The Heck reaction involves the palladium-catalysed arylation of olefinic double bonds (Eqn. (12)) and provides an alternative to Friedel-Crafts reactions for attaching carbon fragments to aromatic rings. 

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... 

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 vinyl positions. The first report on the application of microwave methodology to this type of reaction was published by Hallberg et al. in 1996 [86], Recently, the palladium catalyzed Heck coupling reaction induced by microwave irradiation was reported under solventless liquid-liquid phase-transfer catalytic conditions in the presence of potassium carbonate and a small amount of [Pd(PPh3)2Cl2]-TBAB as a catalyst [87]. The arylation of alkenes with aryl iodides proceeded smoothly to afford exclusively trans product in high yields (86-93%) (Eq. 61). 

With the original protocol, attempted threefold couplings of even a 4-nitro-substituted 1,2,3-triiodobenzene derivative failed.However, under the modified conditions of Jeffery, that is, with a base like potassium carbonate in the presence of a tetrabutylammonium halide, multifold Heck couplings of oligohaloarenes are brought about in very good yields (Schemes 5 and... 

Transition metal catalyzed insertion reactions offer a convenient route for the preparation of five membered heterocyclic rings. Besides intramolecular Heck-couplings and CO insertion, examples of the intramolecular insertion of an acetylene derivative constitute the majority of this chapter. Although some of these processes involve the formation of a carbon-heteroatom bond, they are discussed here. 

In a formally similar reaction an alkene and an alkyne moiety were coupled in the presence of a palladium catalyst in formic acid. The reaction cascade in this case starts by the hydropalladation of the triple bond, which is followed by a Heck-type carbon-carbon bond formation. Running the... 

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 ready insertion of carbon monoxide into furanylpalladium complexes is impressively demonstrated by the reaction depicted in 6.63. The iodofiirane derivative was reacted with carbon monoxide in the presence of tetrabutylammonium chloride. Following an aqueous workup the appropriate carboxylic acid was isolated in good yield (6.63.).94 It is worth pointing out, that due to the mildness of the reaction conditions the Heck coupling of the olefin moiety could be excluded. 

A unique reaction of allenylindium reagents, prepared from propargyl bromides and indium, and haloazines gives rise to the appropriate allenyl-azines. Although the reaction is not a Heck coupling, but a cross-coupling reaction, the aryl moiety is formally attached to a carbon-carbon multiple bond, therefore we mention it here. 

Heck s reaction can result in regioisomers, depending on whether the reaction proceeds at the a or (3 carbons in the alkene. A selectivity > 99% to the a-arylation product was achieved in the Heck coupling of 1-bromonaphthalene to butyl vinyl ether in [bmim][BF4], In contrast, the same reaction in toluene, acetonitrile, DMF, or DMSO... 

Although aryl and vinyl halides have found vast applications in Heck coupling, aromatic diazonium salts, particularly the isolable tetrafluoroborates, proved successful in the work of Kikukawa et al. [23 a, b] and a one-pot reaction with the C-C-coupling step [23 c-e]. Extensions of this tandem diazotation Heck reaction technique were reported by Beller et al. (eq. (5)) [23 f], including heterogeneous Pd/carbon catalysts [23 g]. 

MacNicol et al. (18) [26], have shown interesting inclusion phenomena of which more remains to be explored. Heck coupling has made possible many carbon-rich systems such as the hexaphenylethynylbenzene executed by Heck et al. (19) [27], and the hexaphenylethenylbenzene of de Meijere et al. (20) [28, 29]. This idea has been extended beautifully by Mullen et al. (21) [30] and Moore and Xu (22) [31] in their starburst phenylenes. 

Another method that is widely used for C-C bond formation is the Heck coupling [3]. The arylation of olefinic double bonds is mostly catalyzed by palladium complexes in homogeneous solution. Important advantages of this reaction are the broad availability of arylbromides and chlorides and the tolerance of the reaction for a wide variety of functional groups. There were also developed heterogeneous Pd/C catalysts which exhibit high activity for the Heck reaction of aryl halides with olefins. The reaction conditions are 80 200 °C, solvents (NMP, DMF, tolueneAvater), base addition is necessary (NaOAc, amines, alkali carbonates). The reaction scheme can be described as follows (Eq. 8-22). 

C.i.d. Heck Reaction. 7r-Deflcient chloropyrazines can be Heck-coupled into 1,3-azoles (Scheme 50). It will be recalled that the same methodology was used to couple into the TT-excessive furan, thiophene, and pyrrole heterocycles and their benzo derivatives (vide supra). The Heck reaction in oxazole and thiazole proceeds in a regiospeciflc manner. The new carbon-carbon bond is formed in the 5-position 117 next to the ether heteroatom as commonly observed in vinyl ethers and strongly favored in furan and thiophene. In benzoxazole and benzothiazole the only vacant position is between the two heteroatoms, and the Heck coupling results in substitution into the 2-position 118. " ... 

Although aryl halides and triflates are the most commonly used arylating agents, there are successful examples where both aroyl chlorides and arylsulfonyl chlorides have been employed. Pd-catalyzed decarbonylations and desulfonylations and subsequent Heck couplings are often conducted with trialkylamines such as A-ethylmorpholine as a base, but improved yields are reported in cases in which the tertiary amine is replaced by a mixture of potassium carbonate and benzyltrioctylammonium chloride. In Table 2 two examples are given (entries 17 and 18). ... 

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