Controlling selectivity in N-heterocycle directed borylation of indoles

Abstract

Electrophilic borylation of indoles with BX3 (X = Cl or Br) using directing groups installed at N1 can proceed at the C2 or the C7 position. The six membered heterocycle...

Enhanced N-directed electrophilic C–H borylation generates BN–[5]- and [6]helicenes with improved photophysical properties

“…In contrast the use of only BBr 3 resulted in low yielding (at best) formation of BN–[5]/[6]helicenes under a range of conditions (including forcing conditions). DFT calculations were performed at the M06-2X/6-311+G(d,p) level with a polarisable continuum model (PCM) DCM (this level has provided accurate thermodynamic data in previous calculations on directed electrophilic C–H borylation) 19 to provide insight into this disparity. Note, herein we discuss just the [5]helicene system, but analogous results were found with the parent 2-amino-biphenyl system (see Fig.…”

“…It is also noteworthy to highlight the disparity between facile BBr 3 mediated directed C–H borylation reactions ( e.g. using N-heterocycles or pivaloyl as directing groups) 19,20 versus the much more challenging directed borylation to make 1-Br using just BBr 3 . In other systems, e.g.…”

Transition‐Metal‐Free Heterocyclic Carbon‐Boron Bond Formation

“…Recently, the Ingleson group showed that the modification of the heterocycle directing group attached to indole's nitrogen atom allows selective electrophilic borylation either at the C2 or at the C7 position (Scheme 13d). [75] Sixmembered heterocyclic directing groups like pyridine and pyrimidine, lead to C2 borylation preferentially using BBr 3 . On the other hand, C7 borylation was promoted using fivemembered heterocycle directing groups, such as thiazole and benzoxazole.…”

Enhanced N-directed Electrophilic C-H Borylation Generates BN-[5]- and [6]-helicenes with Improved Photophysical Properties

“…In contrast the use of only BBr3 resulted in low yielding (at best) formation of BN- [5]/ [6]helicenes under a range of conditions (including forcing conditions). DFT calculations were performed at the M06-2X/6-311+G(d,p) level with a polarisable continuum model (PCM) DCM (this level has provided accurate thermodynamic data in previous calculations on directed electrophilic C-H borylation) 19 to provide insight into this disparity. Note, herein we discuss just the [5]helicene system, but analogous results were found with the parent 2-amino-biphenyl system, suggesting the outcomes are general for this type of aminoborane.…”

“…14 It is also noteworthy to highlight the disparity between facile BBr3 mediated directed C-H borylation reactions (e.g. using N-heterocycles or pivaloyl as directing groups) 19,20 versus the much more challenging directed borylation to make 1-Br using just BBr3. In other systems, e.g.…”