Suzuki-Miyaura coupling systems

Miura M (2004) Rational ligand design in constructing efficient catalyst systems for suzuki-miyaura coupling. Angew Chem Int Ed 43 2201-2203... 

Similarly, Pd-mediated sp2-sp2 C—C (Suzuki-Miyaura) coupling has been enabled in biology through the development of an aqueous biologically compatible Suzuki catalyst system [152], This has now allowed the synthetic glycosylation of whole cell surfaces to create bacterial strains with a synthetic glycocalyx [153],... 

In most cases microwave reactions have been conducted in a batch system, but very recently the use of a microflow system for microwave reactions has been reported. For example, Suzuki-Miyaura coupling of aryl halides with phenylboronic acid to form biaryls is promoted by microwave irradiation of the supported Pd catalyst (Table 5.1). A thin, gold film patch located on the outside surface of the base of a glass microreactor is quite effective for absorbing microwaves. 

Suzuki-Miyaura coupling has also been conducted in a capillary reactor (400 i.m inner diameter).A commercial-scale continuous flow system consisting of a 14.5 cm x 25.4 mm column packed with Pd catalyst has also been developed. In this case, supercritical carbon dioxide is used as... 

Figure 8.15 Suzuki-Miyaura coupling in a microflow system having a membrane containing a Pd catalyst...

More recently, Ktigtikbay and co-workers investigated the microwave-assisted Suzuki-Miyaura coupling of 2- and 3-halopyridines using a PdfOAcl /benzimidazo-lium salt catalyst system and K COj as the base. All complexes were reported to have similar activity with the exception of complex 93, which was found to be the least active in Suzuki-Miyaura coupling. In general, heteroaryl chlorides were found to be less reactive than the bromide analogs. In addition, 3-halopyridines were found to couple more efficiently than 2-halopyridines (Table 4). 

Initial research in this area focused on the use of zerovalent Pd2(dba)3 as the palladium source, the carbene IMes, and CS2CO3 as base [43]. This reagent combination afforded a 59% yield in the coupling of 4-chlorotoluene with phenylboronic acid. The catalytic protocol could be simplified by the use of air-stable IMes-HCl that is deprotonated in situ with CS2CO3 isolated yields for the Suzuki-Miyaura coupling then reached >95% (Scheme 8). Subsequently a further simplification of the catalytic system was achieved, by extension of the reaction to air-stable Pd(II) precursors [44]. 

Ohmura et al. [135,136] reported that enantiospeciflc Suzuki-Miyaura coupling reaction of enantioenriched a-(acetylamino)benzylboronic esters with aryl bromides can be switched by the choice of acidic additives in the presence of a Pd/ XPhos catalyst system. Highly enantiospeciflc, invertive C-C bond formation takes place with the use of phenol as an additive as shown in Eq. (8.25). hi contrast, high enantiospeciflcity for retention of configuration is attained in the presence of Zr(0 Pr)4, PrOH as an additive as shown in Eq. (8.26). The reaction proceeds via a cyclization flve-membered ring intermediate of the boron atom. 

The highly reactive catalyst [PdPtBUa] can be generated by fast 1 1 micromixing of [Pd(OAc)2] and PtBUa and can be quickly transferred to the reaction vessel using a flow system to perform the Suzuki-Miyaura couplings [164]. 

The most active NHCP system developed for Suzuki-Miyaura coupling so far was introduced by Shi et al. They investigated the chiral ferrocenyl NHCP system R-8, which was developed by Chung and coworkers for asymmetric hydrogenation (see Section 10.3), because of its resemblance to the famous Josiphos ligand, which, next to its performance in asymmetric catalysis, is also known for... 

Scheme 10.1 First chiral NHCP system used in asymmetric Suzuki-Miyaura coupling.

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