Sterically Controlled Lewis Acid-Base Interaction Toward para-Selective Borylation of Aromatic Aldimines and Benzylamines.

Abstract

Site-selective C-H bond functionalization of arenes at the para position remains extremely challenging primarily due to its relative inaccessibility from the catalytic site. As a consequence, it is significantly restricted to the limited molecular scaffolds. Herein, we report a method for the para-C-H borylation of aromatic aldimines and benzylamines using commercially available ligands under iridium catalysis. The established method displayed excellent para-selectivity for variously substituted aromatic aldimines, benzylamines and bioactive molecules. Based on the several control experiments, it has been realized that a Lewis acid-base interaction between the nitrogen and boron functionality guides the para selectivity via a steric shield for the aromatic aldimines, where Bpin acts as a transient directing group. However, the steric shield of the in situ generated N-Bpin moiety controlled the overall selectivity for the para borylation of benzylamines.