Sequential C−H Borylation and N‐Demethylation of 1,1′‐Biphenylamines: Alternative Route to Polycyclic BN‐Heteroarenes

Abstract Described herein is an unprecedented access to BN‐polyaromatic compounds from 1,1′‐biphenylamines by sequential borane‐mediated C(sp2)−H borylation and intramolecular N‐demethylation. The conveniently in situ generated Piers’ borane from a borinic acid reacts with a series of N,N‐dimethyl‐1,1′‐biphenyl‐2‐amines in the presence of PhSiH3 to afford six‐membered amine‐borane adducts bearing a C(sp2)−B bond at the C2′‐position. These species undergo an intramolecular N‐demethylation with a B(C6F5)3 catalyst to provide BN‐isosteres of polyaromatics. According to computational studies, a stepwise ionic pathway is suggested. Photophysical characters of the resultant BN‐heteroarenes shown them to be distinctive from those of all‐carbon analogues.