Olefination of aryl halides

M. Beller, A. Zapf, and T. H. Riermeier, Palladium-Catalyzed Olefinations of Aryl Halides (Heck Reaction) and Related Transformations, in Transition Metals for Organic Synthesis, Second Ed. (Eds. M. Beller and C. Bolm, Wiley-VCH, Weinheim, 2004, Vol. 1, Chap. 2.13). 

Mechanism of the Olefination of Aryl Halides (Mizoroki-Heck Reaction)... 

Nanometer size Pd colloids in block copolymer micelles of polystyrene polyvinylpyridine as catalysts have been used is a novel way by Klingelhofer for Heck reaction of C-C coupling of aryl halides with olefins. 

The homo-coupling of benzylic halides appears to proceed via benzylnickel intermediates similar to that of aryl halides. The intermediate, benzylnickel halide, was successfully trapped with electron deficient olefins. 

Palladium catalyzed reaction of aryl halides and olefins provide a useful synthetic method for C-C bond formation reaction [171, 172], The commonly used catalyst is palladium acetate, although other palladium complexes have also been used. A sol-vent-free Heck reaction has been conducted in excellent yields using a household MW oven and palladium acetate as catalyst and triethylamine as base (Scheme 6.51) [173], A comparative study revealed that the longer reaction times and deployment of high pressures, typical of classical heating method, are avoided using this MW procedure. 

Among early reported Pd-catalyzed reactions, the Mori-Ban indole synthesis has proven to be very useful for pyrrole annulation. In 1977, based on their success of nickel-catalyzed indole synthesis from 2-chloro-fV-allylaniline, the group led by Mori and Ban disclosed Pd-catalyzed intramolecular reactions of aryl halides with pendant olefins [122]. Compound 102, easily prepared from 2-bromo-lV-acetylaniline and methyl bromocrotonate, was adopted as the cyclization precursor. Treatment of 102 with Pd(OAc)2 (2 mol%), Ph3P (4 mol%) and NaHCQ3... 

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]. 

This article presents the principles known so far for the synthesis of metal complexes containing stable carbenes, including the preparation of the relevant carbene precursors. The use of some of these compounds in transition-metal-catalyzed reactions is discussed mainly for ruthenium-catalyzed olefin metathesis and palladium-Znickel-catalyzed coupling reactions of aryl halides, but other reactions will be touched upon as well. Chapters about the properties of metal- carbene complexes, their applications in materials science and medicinal chemistry, and their role in bioinorganic chemistry round the survey off. The focus of this review is on ZV-heterocyclic carbenes, in the following abbreviated as NHC and NHCs, respectively. 

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... 

Since Wakamatsu serendipitously discovered amidocarbonylation while performing the cobalt-catalyzed hydroformyla-tion of olefins in 1971, this unique carbonylation reaction, affording a-amino acids directly from aldehydes, has been extensively studied.More recently, palladium-catalyzed processes have been developed to expand the scope of this reaction.The Pd-catalyzed amidocarbonylation has been applied to aldehydes,aryl halides, and imines. As a related reaction, lactamization " of aryl halides catalyzed by a rhodium complex has also been developed. 

In addition to the Suzuki-Miyaura reaction, the authors also found the catalyst 136 to be active toward the arylation of olefins with aryl halides as illustrated in Table 20. Again to conduct a reaction, the authors circulated a solution containing 4-iodoacetophenone 138 (1.00 mmol), the alkene (3.00 mmol) under investigation, and tributylamine 139 (3.00 mmol) in anhydrous DMF (3 ml), through the heated reactor (120 °C) at a flow rate of 2 ml min After 24h, the flow reactor was rinsed with DMF and the... 

The general catalytic cycle in Heck-type polycondensation consisting of the oxidative addition of aryl halide, olefin insertion and reductive elimination is shown in Figure 8.2 [100-104]. 

Electrochemical reduction of aryl halides in the presence of olefins (94), (equation 54) leads to the formation of arylated products (95). Electroreduction of several aralkyl halides at potentials ranging from -1.24 V to -1.54 V (see) gives products which involve dimerization, cyclization, and reduction to the arylalkanes. Carbanions and/or free radicals were again postulated as intermediates79. Aryl radicals generated from the electrochemical reduction of aryl halides have been added to carbon-carbon double bonds80,81. Electrochemical reduction of aryl halides in the presence of olefins leads to the formation of arylated products78. Preparative scale electrolyses were carried out in solvents such as acetonitrile, DMF and DMSO at constant potential or in liquid ammonia at constant current. The reaction is proposed to involve an S l mechanism. 

Palladium-catalyzed vinylations of aryl halides are generally referred to as the Heck reaction (for reviews on the Heck reaction see [34-40]), a versatile process that can be performed inter- and intramolecularly [41]. In the Heck reaction the carbon-carbon single bond forming step is an insertion of an al-kene into the aryl-Pd bond, i.e., a carbopalladation, giving rise to an alkyl-Pd species. If this insertion is terminated by /1-hydride elimination the expected vinylation product is the outcome of the classical Heck reaction. Likewise, reversible insertion of a highly strained olefin where the /1-hydride elimination is suppressed leads to an entry to multiple Pd-catalyzed bond forming processes. 

The perfluoroaikylcopper reagents have found extensive application as perfluoroalkylation reagents Typical examples of perfluoroalkylation of aryl halides have been illustrated in table 6 These perfluoroaikylcopper reagents readily couple with vinyl iodides and vinyl bromides [220, 221, 222] Typical examples of mono- orbisvmylic coupling are shown in equations 148 and 149 When 1-bromo-1 -perfluoroalkylethy lenes were reacted with perfluoroaikylcopper compounds, the expected gew-disubstituted olefin was not formed, but the vic-disubshtuted product was obtained [223] (equation 150)... 

Nickel(O) triphenylphosphine species have been used to convert allyl halides to 1,5-hexadiene [332], for the reductive coupling of ethylene with aryl halides to give 1,1-diaryl-ethanes [333], and for the coupling of aryl halides and alkenes to prepare substituted olefins [334], In addition, l,2-bis[(di-2-propylphosphino)benzene]nickel(0) has been used for the reductive coupling of aryl halides [335], and l,2-bis[(diphenylphosphino)ethane]-nickel(O) has been employed to synthesize biphenyl from bromobenzene [336] and to prepare benzoic acid from bromobenzene in the presence of carbon dioxide [337]. 

If secondary and tertiary amines are desired, only 2 to 3 moles of ammonia are used. Aqueous ammonia does not react to any extent at room temperature, owing to the immiscibility of halide and water. Industrially, aqueous ammonia is used and heated in an autoclave under pressure. Tertiary halides, as, for example, tert-butyl and tert- m.y bromides, do not yield amines, but yield olefines almost exclusively. The object of the present experiment is to illustrate the ammonolysis of alkyl halides. The ammonolysis of aryl halides cannot be easily accomplished in the laboratory, as it involves the use of high pressure, and temperatures of about 200°. Industrially the method is practical. 

An alternative to the coupling of olefins with aryl halides is C-H activation of benzenes and addition to alkynes. A Pd" catalyst was shown to catalyze this reaction in an acidic medium such as CF3COOH, even at room temperature (eq. (17)) [83],... 

Palladacycles prepared by the addition of furancarbothioamide to a methanol solution of Li2PdCl4 at room temperature are soluble in hexane, chloroform, and moderately soluble in polar solvents DMF and DMSO [187]. These palladacycles are thermally stable, not sensitive to air or moisture, and can be applied effectively in the Heck reaction of aryl halides with terminal olefins and in the Suzuki reaction of aryl halides with arylboronic acids. These reactions were performed under aerobic conditions, leading to turnover numbers... 

In 1984, Hegedus and Harrington reported a synthesis of 3- and 4-substituled indoles [77] employing Heck s well-established process Pd(O)-catalyzed functionalization of aryl halides by the oxidative addition-olefin insertion-P-hydride elimination. In this instance. 4-bromo-I-tosylindole (161, Scheme 28) was converted to several diversely functionalized 4-substituted I-tosylindoles. Selective electrophilic substitutions at the C(3) position of 161 provided access to 3-(chloromcrcurio)-l-tosylindole and 3-iodo-l-tosylindole (162), which then underwent a Heck... 

Carbonylation of olefins and aryl halides to the corresponding esters or amides find in ILs an ideal media for the palladium-catalysed process. 

The palladium-catalysed arylation of olefins with aryl halides, the Heck reaction, is usually performed in polar solvents such as acetonitrile or dimethyl sulfoxide, in combination with a base and a Pd(ii) pre-catalyst that may or may not be associated with a phosphorus ligand. Given that quaternary ammonium or phosphonium salts are known to increase reaction rates, ILs emerged as promising solvents for this reaction.In the case of imidazolium-based ionic liquids, the solvent, beside providing an unusual coulombic environment. 

The palladation products exhibit reactivity similar to that of the arylpalladium complexes formed by oxidative addition of aryl halides to Pd(0) species, although the reactions are stoichiometric with respect to palladium. Representative examples include vinylation via an olefin insertion process (eq (88)) [119], double and single carbonylation (eq (89) and (90)) [120,121], and alkylation via a transmetallation process (eq (91)) [122]. 

In 1991 at the Central Research Laboratories of Hoechst AG we became interested in the palladium-catalyzed olefination (Heck reaction) of aryl halides and aryl diazonium compounds which is arguably one of the most powerfiil methods for the synthesis of substituted olefins. In collaboration with Herrmann and co-workers we have shown that active catalyst mixtures obtained by using in situ mixtures of Pd(II) salts and commercially available tri-o-tolylphosphine consist under the conditions of the Heck reaction primarily of cyclometaUated paUadacycles l... 

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