Efficient Modular Synthesis of Substituted Borazaronaphthalene

A highly efficient modular synthetic method for BN-fused polycyclic aromatic hydrocarbons (PAHs) composed of a borazaronaphthalene core along with multiple functionalized sites is reported. The halogenated 2,1-borazaronaphthalene cores are constructed through a ring-closing reaction between o-ethynylaniline derivatives and boron halides. The controllable halogen substituents make further derivatization of 2,1-borazaronaphthalene cores feasible by using metal-catalyzed cross-coupling reactions. On the basis of the carefully designed precursors, various functional aromatic rings can be fused to the azaborine core via a one-pot nucleophilic tandem reaction, affording previously inaccessible PAHs in moderate yields.