Arylation Heck coupling

Finally, a tandem jV-arylation/Heck coupling has also been developed for indole synthesis. Vinologous amide 11 couples with aryldibromide 10 to... 

Buchwald et al. employed a domino arylation/Heck coupling to access diben-zoazepines. Palladium loadings of 1.5 mol% with 2.25 mol% of 22b were necessary to ensure high yields (Scheme 13.95) [141]. 

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. 

The coupling reaction of aryl-alkenyl halides with alkenes in the presence of a palladium catalyst and a base is known as the Heck coupling (Scheme 9.4).6 Since the early 1980s, this type of coupling reaction has been used for die syndiesis of poly(arylenevinylene) and related polymers by polymerization of AB- or AA/BB-type of monomers (Scheme 9.5).7... 

HECK COUPLINGS OF ACTIVATED ARYL CHLORIDES AT ROOM TEMPERATURE... 

Thus, in terms of scope, mildness, and convenience, Pd/P( -Bu)3 provides an attractive method for achieving Heck couplings of aryl chlorides. 

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. 

To overcome this drawback, we studied the arylation of diethyl 2-vinyl-[l,3]-dioxolane-4,5-diacetate 2 with several bromo polyaromatic and heteroaromatic substrates (Table 21.1 and Scheme 21.4). In parallel, the Heck coupling of several vinyl dioxolane derivatives with aryl bromides was studied in the presence of homogeneous catalysts (Table 21.1). 

Heck coupling of aryl halides with n-butylacrylate under m/w irradiation. 

Interestingly, treatment of diene 215a with methanesulfonic acid afforded 216 as a single diastereomer in 88% yield, the structure of which was confirmed by X-ray analysis (Scheme 60). The transformation of 216 into 217 started with an alkylation, followed by reductive desulfurization and triazene formation to afford compound 217 in 92% yield. Upon treatment with diiodomethane, triazene 217 was smoothly converted to aryl iodide 218 in 75% yield. Pd-catalyzed intramolecular Heck coupling of 218 led to the desired product 219b in 62% yield. 

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). 

A perhaps more exotic substrate for the Heck reaction is 1,2-cyclohexanedione [25], The reactivity of this molecule under Heck coupling conditions can probably be attributed to its resonance enol form. This reaction is attractive, because the literature contains relatively few examples of the preparation of 3-aryl-l,2-cyclohexane-diones. Yields varied from good to modest when classic heating and electron-rich aryl bromides were used, and reaction times typically ranged from 16 to 48 h. Similar yields were obtained under continuous microwave irradiation with a single-mode microwave reactor for 10 min at 40-50 W (Eq. 11.10) [25],... 

The vinyl triflate of Komfeld s ketone has been subjected to Heck reactions with methyl acrylate, methyl methacrylate, and methyl 3-(Af-rerf-butoxycarbonyl-lV-methyl)amino-2-methylenepropionate leading to a formal synthesis of lysergic acid [259]. A similar Heck reaction between l-(phenylsulfonyl)indol-5-yl triflate and dehydroalanine methyl ester was described by this research group [260]. Chloropyrazines undergo Heck couplings with both indole and 1-tosylindole, and these reactions are discussed in the pyrazine Chapter [261], Rajeswaran and Srinivasan described an interesting arylation of bromomethyl indole 229 with arenes [262]. Subsequent desulfurization and hydrolysis furnishes 2-arylmethylindoles 230. Bis-indole 231 was also prepared in this study. 

Arylation of cycloalkenes.1 Aryl halides undergo Heck coupling with cy-cloalkenes in the presence of a palladium catalyst. The reaction involves addition of an arylpalladium intermediate to the double bond followed by elimination of a palladium hydride. 

E)-stilbene was the exclusive product of the Pd colloid-catalyzed Heck arylation of styrene with chlorobenzene. Recently, a polymer-mediated self-assembly of functionalized Pd and Si02 nanoparticles have been found to be highly active catalysts for hydrogenation and Heck coupling... 

Table3. Results obtained from Heck coupling of n-butylacrylate (BA) with aryl halides (X = halide, and R = para substituent) under various conditions using 3-5 mol % Pd...

Olefin that undergoes dihydroxylation is generated in situ from aryl halide and a terminal olefin via Pd-catalyzed Heck coupling. 

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