Sequential C-H Borylation and N-Demethylation of 1,1'-Biphenylamines: Alternative Route to Polycyclic BN-Heteroarenes.

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(C6 F5 )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.