Pd-Catalyzed Direct Arylation of Tautomerizable Heterocycles with Aryl Boronic Acids via C-OH Bond Activation Using Phosphonium Salts

摘要

Biaryl compounds (Ar-Ar) have become increasingly important building blocks in materials and Pharmaceuticals.1 Transition-metal-catalyzed biaryl cross-coupling of arenes or heterocycles (Ar-H) have proven to be an exceedingly valuable process in contemporary organic synthesis developed in the past decades. Traditional biaryl synthesis involves the coupling of activated Ar-H (Ar-X) and metalated Ar-H (Ar-M) (Scheme 1). Preparation of both coupling partners usually requires multisteps including protection of the sensitive functional groups in the substrates if necessary. This generates waste from reagents, solvents, and purifications. Direct arylation is a new type of cross-coupling between an unactivated and unprotected substrate and one of the traditional coupling partners (Ar-X or Ar-M). In recent years, direct arylation via C-H bond activation has emerged as an attractive alternative approach to traditional cross-coupling methods, and has led to a number of reactions that utilize directing groups, repulsive steric interactions, electron-rich substrates or C-H bond acidity, through the coupling of Ar-H with either Ar-X or Ar-M.