Arylboronate arylating agent

Instead of aryl halides, arenediazonium salts are also excellent arylating agents in the Suzuki coupling, although more hindered arylboronic acids did not react The reaction is catalysed by several sources of ligand-free palladium such as Pd(OAc)2, Pd2(dba)3 and Pd/C at room temperature in dioxane without any added base [98]. Use of potassium aryl trifluoroborate salts also allowed the introduction of more sterically hindered aryl groups [99]. 

Several solvent-free N-alkylation reactions have been reported which involve use of tetrabutylammonium bromide (TBAB), as a phase-transfer agent, under micro-wave irradiation conditions, an approach that is developed in Chapter 6 [36]. An experimentally simple microwave-assisted solvent-free N-arylation of primary amines with sodium tetraphenylborate or arylboronic acids, promoted by inexpensive cupric acetate on the surface of KF-alumina, has been reported. The reaction is selective for mono-N-arylation and a variety of functional groups are tolerated in the process (Scheme 8.4) [37]. 

Ito designed a metal-free approach to the borylation of aryl halides using a silylborane as the borylating agent (Scheme 6.33) [3]. The reaction conditions were quite mild, and a host of functionalized aryl halides were converted into arylboronates. Substrates bearing esters, halogens, amides, and unprotected amines were well tolerated. The chanistry also converted bulky aryl halides into arylboronates. For example, bromo-2,4,6-triisopropylbenzene... 

Classic approaches to this chemistry start from aryl halides and an oxidizing agent such as MCPBA [160, 161]. If an arylboronic acid is available, it is also a convenient entry point to the chemistry [96]... 

NiCl2(PCy3)2 associated with PCyj promotes the selective cross-coupling of aryl-tosylates with arylboronic acids under relatively mild conditions, and a variety of function groups are tolerated in both arenes [70]. It is particularly noteworthy that no reducing agent such as Zn is required in this reaction. More recently, room-temperature nickel-catalyzed Suzuki coupling reactions of arenesulfonates with arylboronic acids have been disclosed [71]. 

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