Arylation activated olefins

Aryl and vinylic bromides and iodides react with the least substituted and most electrophilic carbon atoms of activated olefins, e.g., styrenes, allylic alcohols, a,p-unsaturated esters and nitriles. 

The reactions of enamines with positively activated olefins have been extended to arylations with />-quinones (350,362-369) and quinone sulfoni-mides (365-368,370). Thus a new pathway for the facile formation of benzofurans and indoles became available. 

Catalytic processes based on the use of electrogenerated nickel(O) bipyridine complexes have been a prominent theme in the laboratories of Nedelec, Perichon, and Troupel some of the more recent work has involved the following (1) cross-coupling of aryl halides with ethyl chloroacetate [143], with activated olefins [144], and with activated alkyl halides [145], (2) coupling of organic halides with carbon monoxide to form ketones [146], (3) coupling of a-chloroketones with aryl halides to give O -arylated ketones [147], and (4) formation of ketones via reduction of a mixture of a benzyl or alkyl halide with a metal carbonyl [148]. 

The conjugated addition of aryl bromides to activated olefins has... 

TaUe 10. Electroreductive arylation of activated olefins using Ni-pyridine as catalyst... 

The direct carboxylation of unsaturated compounds has already been reported [107,108]. The process is however limited to reducible alkenes like aryl olefins or activated olefins. On the other hand, only a few examples of direct electrocarboxylation of alkynes have been reported [109],... 

In a series of investigations [140-146], Gomes etal. utilized cobaltous bromide (although some work was done with cobaltous chloride) as a precursor for the catalytic reduction of aryl halides in the presence of activated olefins to afford... 

Electroreduction of the cobalt(II) salt in a mixture of either dimethylform-amide-pyridine or acetonitrile-pyridine as solvent, often in the presence of bipyridine, produces a catalytically active cobalt(I) complex which is believed to be cobalt(I) bromide with attached bipyridine ligands (or pyridine moieties in the absence of bipyridine). As quickly as it is electrogenerated, the active catalyst reduces an aryl halide, after which the resulting aryl radical can undergo coupling with an acrylate ester [141], a different aryl halide (to form a biaryl compound) [142], an activated olefin [143], an allylic carbonate [144], an allylic acetate [144, 145], or a... 

Reaction of l-aryl-3-carbethoxy-6-phenyl-l,4,5,6-tetrahydropyridazin-4-ones 718 with activated olefins such as benzalacetophenone, benzalacetone, 3-benzylideneacetylacetone, diethyl 2-benzylidenemalonate, and a-cyano-/3-phenylacrylic acid in the presence of an organic base like pyrrolidine, morpholine, piperidine, or triethylamine gave the corresponding 2,8-dihydro-l//-pyrano[2,3-t7 pyridazines 719-723, respectively. The 1-oxo- and 1-imino derivatives of the pyrano[2,3-r/ pyridazine ring system were also prepared from the respective 6-oxo or 6-imino derivative of the starting pyridazine 718 under the same conditions (Equation 60) <1989IJB733>. 

The amount of cobalt complex in this step influences the reaction rate, but not the yields. Indeed, with only 0.3 equivalent of cobalt catalyst, the arylzinc compound is consumed after 24 h instead of 10 h when 1 equivalent was used. An excess of the activated olefin is required to optimize the yield of the conjugate addition. Under these conditions, this process has been studied with various aryl halides (X = Br, Cl) and activated olefins. Yields range from 40 to 80%. 

At the beginning of the new millennium, Hashmi et al. presented a broad research study on both intramolecular and intermolecular nucleophilic addition to alkynes and olefins [18]. One of the areas covered by these authors was the isomerization of co-alkynylfuran to phenols [19]. After that, Echavarren and coworkers identified the involvement of gold-carbene species in this type of process, thus opening a new branch in gold chemistry [20]. And subsequently, Yang and He demonstrated the initial activation of aryl —H bonds in the intermolecular reaction of electron-rich arenes with O-nucleophiles [21, 22]. 

The method is quite useful for particulary active alkyl halides such as allylic, benzylic, and propargylic halides, and for a-halo ethers and esters, but is not very serviceable for ordinary primary and secondary halides. Tertiary halides do not give the reaction at all since, with respect to the halide, this is nucleophilic substitution and elimination predominates. The reaction can also be applied to activated aryl halides (such as 2,4-dinitrochlo-robenzene see Chapter 13), to epoxides,217 and to activated olefins such as acrylonitrile, e.g.,... 

Arylation of Activated Olefins by Diazonium Salts. Meerwein Arylation Arylation or Aryl-de-hydrogenation... 

Free-radical addition of an aryl group and a hydrogen has been achieved by treatment of activated olefins with a diazonium salt and TiClj.54-1... 

The most widely used version of the Heck reaction is the coupling of aryl bromides or iodides with activated olefins such as styrene or acrylic acid derivatives, using conditions first described by Spencer [18], The catalysts are generated in situ by combining Pd(OAc)2 with two to four equivalents of triphenyl- or tri-o-tolyl-phosphine. Triethylamine, K2C03, NaHC03, or NaOAc are often used as the base. 

The efficient conjugate addition-type arylation of activated olefins has not been achieved by the use of copper-catalyzed reactions. This situation was circum-... 

The three component aminoallylation reaction of the activated olefins 4 was also reported by us (Scheme 7) [39]. The palladium catalyzed reaction between phthalimid 10, olefins 4 and allyl chloride 11 proceeded well in the presence of CS2CO3 to give the corresponding aminoallylation products 12 in high yields. Likewise, cyanoallylation of activated olefins was also reported (Scheme 8) [40]. In both cases only aryl substituded and f-bulyl substituded olefins are proved good substrates. The mechanism of these reactions is presumably similar to that of hydroalkoxylation reaction (see Scheme 5). 

The palladacyle formed in the latter reaction is a highly active catalyst precursor for the Heck arylation of activated olefins the Pd11 species is converted into a Pd° phosphine complex under catalytic conditions.37... 

This Chapter is subdivided into five Sections dealing with alkylation and related reactions activation of aryl and vinyl halides by transition metals to manufacture fine chemicals butadiene chemistry olefin oligomerization car-bene chemistry and asymmetric cyclopropanation. 

Brunner, H., Bluchel, C., Doyle, M. P. Asymmetric catalysis. Part 108. Copper catalysts with optically active ligands in the enantioselective Meerwein arylation of activated olefins. J. Organomet. Chem. 1997, 541, 89-95. 

During the past decade, considerable progress has been made in the area of transition metal-catalyzed cleavage and functionalization of the inert C-Cl bond in nonactivated chloroaromatic compounds. This new and important field of chemistry is reviewed in the present chapter, which describes both mechanistic and synthetic aspects of C-Cl activation. Oxidative addition reactions of chloroarenes to complexes of catalytic metals are discussed, along with their applications in a wide variety of reductive dechlorination, nucleophilic displacement, olefin arylation, coupling, and carbonylation reactions. 

When stripped to its naked minimum, the thermal chemistry of aryl azides is deceptively simple. Excluding those compounds bearing reactive ortho substituents [3] and reactions carried out in the presence of active olefins [4], the thermolysis of an aryl azide simply causes unimolecular loss of nitrogen. The complexity arises in subsequent steps where intervention of the various intermediates shown in Figure 1 has been postulated to precede formation of isolatable products. The photolysis of aryl azides is further complicated by the inclusion of reactions originating from electronically excited singlet and triplet states of the azide itself [5]. In essence, a clear understanding of aryl azide chemistry requires the description of the participation and role of each of these reactive intermediates under various reaction conditions. 

Nickel halides catalyze the conversion of unreactive aryl chlorides into aryl iodides by Nal in DMF at 140 °C. In the presence of a palladium catalyst and an activated olefin, the aryl iodide is transformed into the Heck coupling product. Nickel(O) complexes are poor catalysts for the coupling step. The halide exchange is thought to be a radical reaction since it is suppressed by the addition of 5% p-dinitrobenzene as radical scavenger. While nickel catalysts do not perform... 

The Wang group also realized enantioselective oxidative cross-coupling reactions between tertiary amines and the activated olefins by merging Cu(OTf)2 with quinine as the best cooperative catalysts/ A Morita-Baylis-Hillman-type mechanism is in operation. It was notable that molecular oxygen was employed as the sole oxidant. As shown in Scheme 2.12, the reactions between Ai-aryl THIQs and the a,p-unsaturated aldehydes or ketones 30 proceeded smoothly to afford the a-functionalized products 31 in up to 81% yield and 99% ee. 

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