Nickel-Catalysed Mizoroki-Heck-Type Reactions

3 Nickel-Catalysed Mizoroki-Heck-Type Reactions 

Recently, an efficient nickel catalyst for arylation reactions of acrylates was developed by Inamoto et al. [37] that relies on the in-situ generation of an A-heterocyclic carbene 

8 Nickel-catalysed Mizoroki-Heck-type reaction with electrochemical 

NiCl2-6 H20(34) (1.0mol%) PPh3 (35) (2.0 tnol%) Na2C03 (1.3 equiv) 

For some applications, the use of homogeneous catalysts can generally cause significant practical problems, since the separation of products from the catalysts, as well as their recyclability, can be rather difficult to achieve. Therefore, Arai and coworkers [40] probed various transition metal salts in a biphasic reaction mixture for the arylation of butyl acrylate (18) with iodobenzene (13). The biphasic reaction system consisted of ethylene glycol and toluene. Under otherwise identical reaction conditions, the following reactivity trend was 

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Generally applicable nickel-catalysed arylation reactions of alkenes were accomplished through the use of relatively strong stoichiometric reducing reagents [29]. Hence, Perichon and coworkers [30] developed an electrochemical, highly selective nickel-catalysed Mizoroki-Heck-type reaction (Scheme 10.8). Importantly, this early report showed that not only aryl iodides and bromides, but also less reactive aryl chlorides could be used for luckel-catalysed Mizoroki-Heck-type reactions. 

Scheme 10.9 Nickel-catalysed MIzoroki-Heck-type reaction with stoichiometric amounts of Zn (27).

Scheme 10.16 Nickel-catalysed Mizoroki-Heck-type reactions with TPPTS (53) as ligand.

The use of pyridine (31) as additive allowed for more selective and efficient nickel-catalysed arylations of styrenes (Scheme 10.10) [32, 33]. Aryl and alkyl bromides gave good yields of isolated products. With respect to the latter, secondary alkyl bromides proved superior to primary ones. However, use of methyl acrylate (1) as substrate yielded predominantly products originating from conjugate additions, rather than Mizoroki-Heck-type reactions. 

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