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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
The Heck reaction is a palladium-catalyzed vinylation of organic halides (Scheme I), forming a carbon–carbon bond. Various organic halides, such as aryl, heterocyclic, benzyl, or vinyl bromides or iodides, can be utilized in this reaction. Organic halides with β-hydrogen atoms can not be used because the β-elimination will lead to the formation of an olefin under the normal Heck reaction conditions. A base is necessary to remove the hydrogen halide so that the catalytic cycle can be completed. When organic bromide is used, a ligand such as triarylphosphine or a secondary amine is required.
MMT Intercalated Pd Nanocatalyst for Heck (Mizoroki-Heck) Reaction
Published in V. R. Remya, H. Akhina, Oluwatobi Samuel Oluwafemi, Nandakumar Kalarikkal, Sabu Thomas, Nanostructured Smart Materials, 2022
Prashant Gautam, Vivek Srivastava
The coupling reactions have started a new era of chemical transformation and become an important transformation for carbon-carbon bond-forming reactions. Heck, Suzuki, Sonogoshira, Negishi, Kumada, Stille, Tsuji-Trost, etc., have played an important role to shape chemical synthesis [1–4]. Among different types of the coupling reaction, the Heck reaction is extensively applied in the synthesis of agrochemical, pharmaceutical, and fine chemical, etc., [2, 3]. Heck procedure is striking from a synthetic point of view as it offers a high degree of chemoselectivity and easy reaction settings.
Metal-Catalyzed Condensation Polymerization
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
Heck coupling, also called Mizoroki–Heck reaction, involves reaction of vinyl/aryl/benzyl halide or triflate with an alkene (electron deficient) in the presence of a base and a Pd catalyst to form a substituted alkene. The reaction follows the same catalytic cycle for palladium(0)-catalyzed reactions as described earlier. Heck coupling is used to synthesize poly(phenylene vinylene) (PPV)-based conjugated polymers that contain alternating phenyl rings and C=C bonds.
Fluorescent bent-core mesogens with thiophene-based central unit
Published in Liquid Crystals, 2020
Joanna Matraszek, Katarzyna Grześkiewicz, Ewa Górecka, Damian Pociecha
The materials 1–4 were obtained by several synthesis steps presented in Figure 1. Two key steps were palladium-catalysed cross-coupling Suzuki-Miyaura reaction and Heck reaction. The side-arms were synthesised according to previously described procedure [22]. The first step of the synthesis of the central part of the molecules was Suzuki reaction under typically conditions [23], followed by the transformation of the resulting dialdehydes A into divinyl compounds B via Wittig reaction [24]. 2,5-bis(vinylphenyl)-3-hexylthiophene or 2,5-bis(vinylphenyl)-3-methylthiophene B was connected with iododerivative to yield banana-shaped molecules of the family 1–4. For the Heck coupling various conditions were tested to get final product in good yield. When ionic liquid was used as a solvent, palladium acetate as a catalyst and potassium phosphate as a base [25] the desired product was obtained but the purification was a serious problem. Using tri-o-tolylphosphine (TolPh) and triethyloamine as a solvent and base the reaction yield was poor. A significant increase in the yield of the product – from 20% to 45% – was observed when the reaction was performed in a mixture of anhydrous dimethylformamide and triethylamine. This mixture of solvents, the presence of palladium acetate and tri-o-tolylphospine at 110°C was found to be optimal for efficiency of this reaction [26].
Copper-assisted synthesis of five-membered O-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Yamini Verma, Neha Ahlawat, Pooja Grewal, Pranshu Bhardwaj, Nirmala Kumari Jangid
It was reported that the reaction was not effectively catalyzed with cuprous bromide, cuprous iodide, or cuprous chloride and 2-phenylbenzo[b]furan was obtained in 10%, 10%, and 20%, respectively. The 2-phenylbenzo[b]furan was not obtained when the reaction occurred without [Cu(phen)(PPh3)2]NO3 or cesium carbonate. Therefore, cesium carbonate was used as a base and [Cu(phen)(PPh3)2]NO3 as a catalyst to produce 2-arylbenzo[b]furans from aryl acetylenes and o-iodophenols in toluene. The efficacy of this method was examined when various aryl acetylenes was coupled with o-iodophenol. This strategy was utilized to couple the o-iodophenol with electron-poor and electron-rich aryl acetylenes in good to excellent yields. This reaction tolerated base-sensitive functional groups like methyl esters and methyl ketones.[125] The coupling of o-substituted aryl acetylenes with o-iodophenol occurred in good yields. An alkene containing aryl acetylenes were also coupled in good yields without Heck-like coupling; the Heck reaction occurred if Pd was used (Scheme 41).
Fluorescent liquid crystals with rod-shaped π-conjugated hydrocarbon core
Published in Liquid Crystals, 2019
Jens Buchs, André Geßner, Benjamin Heyne, Dietmar Janietz, Hans Sawade
The synthesis of the bis(phenylenevinylene) compounds 3–6 is outlined in Scheme 1. The 4-alkoxybenzaldehydes 1 were prepared by alkylation of 4-hydroxy-benzaldehyde with the respective alkyl bromides in the presence of potassium carbonate. The alkoxy substituted styrenes 2 were obtained in a Wittig reaction using a methyltriphenylphosphonium salt from the benzaldehydes 1. Finally, a Heck reaction [43] between the styrenes 2 and the appropriate dibromoarenes using a catalytic amount of palladium acetate afforded the bis(alkoxyphenylethenyl)arenes 3–6.