Nickel‐Catalyzed Cross‐Coupling of Phenols and Arylboronic Acids Through an In Situ Phenol Activation Mediated by PyBroP

Abstract

A new method for the Suzuki-Miyaura cross-coupling of phenols and arylboronic acids through in situ phenol activation mediated by PyBroP is presented. The reaction proceeds efficiently by using cost-effective, markedly stable [NiCl(2)(dppp)] (dppp=1,3-bis(diphenylphosphino)propane) as the catalyst in only 5 mol % loading, as well as in the absence of extra ligands. The method exhibits broad applicability and high efficiency towards a wide range of both phenols and boronic acids, including activated, nonactivated, deactivated, and heteroaromatic coupling partners. In addition, various functional groups, such as ether, amino, cyano, ester, and ketone groups, are compatible with this transformation. Notably, arylboronic acids containing an unprotected NH(2) group and 2-heterocyclic boronic acids, which are generally problematic for coupling under conventional conditions, are also viable substrates, although moderate yields were obtained for sterically hindered substrates. Consequently, the in situ cross-coupling methodology coupled with the use of an inexpensive and stable nickel catalyst provides a rapid and efficient pathway for the assembly of biaryls and heterobiaryls with structural diversity from readily available phenol compounds.

Well-defined nickel and palladium precatalysts for cross-coupling

“…The yields are similar to those using other systems but can be obtained using a significantly lower precatalyst loading (1–1.5 mol% compared with >5 mol%). Unique to this precatalyst is its ability to couple phenols through in situ derivatization using bromotripyrrolidinophosphonium hexafluorophosphate (PyBroP) in the same pot as boronic acids 122 . Borylations of heteroaryl bromides, chlorides, mesylates, tosylates, triflates and sulfamates using the boron reagent tetrahydroxydiboron are also possible using a remarkably low catalyst loading of only 1 mol% 123 .…”

Nickel-Catalyzed Cross-Coupling Reactions of Unreactive Phenolic Electrophiles via C–O Bond Activation

“…Such a process could be possible by the in situ conversion of arenols into activated forms such as sulfonates or phosphonium [104,105] through the addition of stoichiometric amounts of activating reagents. Because of space limitations, this section only deals with the nickel-catalyzed direct transformation of arenols using non-classical stoichiometric activating reagents.…”

Functionalization of some benzylthioarylboronic acids by benzylic lithiation of their N‐butyldiethanolamine esters or lithium (triisopropoxy)borates

“…[9] Our work deals with benzylic lithiation of tetravalent arylboron complexes containing sulfuractivated benzylic hydrogen atoms. The obtained borio-lithio derivatives can be easily converted into various functionalized arylboronic acids that can be used in coupling reactions [10,11] or tested as saccharides sensors. [12,13] …”