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.

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

“…The X-ray structures shown with thermal ellipsoidsa t50% probability. [19] Angewandte Chemie Zuschriften noteworthy that these BÀNbond lengths are shorter than that (1.464 )o fap reviously reported B 2 N 2 -triphenylene, [4d] and such shorter B À Nbonds in 3 can be attributed to the presence of an electron-withdrawing C 6 F 5 group on B.…”

“…[19] The selected bond lengths of B-N are 1.634 (entry 2), 1.650 (entry 4, 2a), and the B-P is 1.972 (entry 7). [19] The selected bond lengths of B-N are 1.634 (entry 2), 1.650 (entry 4, 2a), and the B-P is 1.972 (entry 7).…”

“…[19] the C4'-position (1a-i)r eadily reacted with Piers borane to provide as eries of 2'-mono-boryl-1,1'-biphenylamines in 63-97 %y ields (2a-i). [19] the C4'-position (1a-i)r eadily reacted with Piers borane to provide as eries of 2'-mono-boryl-1,1'-biphenylamines in 63-97 %y ields (2a-i).…”

“…[b] ORTEP with thermal ellipsoidss et at 50 %probability level. [19] The selected bond lengths of B-N are 1.634 (entry 2), 1.650 (entry 4, 2a), and the B-P is 1.972 (entry 7). [c] Piers' borane was pregenerated in situ prior to addition of 1a.…”

“…[b] For48h.The X-ray structures shown with thermal ellipsoidsat50% probability. [19] Angewandte Chemie Zuschriften the C4'-position (1a-i)r eadily reacted with Piers borane to provide as eries of 2'-mono-boryl-1,1'-biphenylamines in 63-97 %y ields (2a-i). Noteworthy is that the present procedure is also operative on a( semi)gram scale with good to high yields (2a and 2e).…”