Chiral Bidentate Boryl Ligand Enabled Iridium-Catalyzed Asymmetric C(sp2)-H Borylation of Diarylmethylamines.

Abstract

Optically active organoboronic acids and their derivatives are an important family of target compounds in organic chemistry, catalysis, and medicinal chemistry. Yet there are rare asymmetric catalytic examples reported for the synthesis of these compounds via atom and step economic ways. Herein, we report a chelate-directed iridium-catalyzed asymmetric C(sp2)-H borylation of aromatic C-H bonds directed by free amine groups. The success of these transformations relies on a novel family of chiral bidentate boryl ligands (L).They can be synthesized straightforwardly in three steps starting from readily available ( S, S)-1,2-diphenyl-1,2-ethanediamie (( S, S)-DPEN). The Ir-catalyzed C(sp2)-H borylation comprises two parts. The first part is desymmetrization of prochiral diarylmethylamines. In the presence ofL3/Ir, a vast array of corresponding borylated products were obtained with high regioselectivity and good to excellent enantioselectivities (26 examples, up to 96% ee). The second part, kinetic resolution of racemic diarylmethylamines, was also conducted. Good selectivity values (up to 68%, 11 examples) were obtained whenL8 was used. We also demonstrated the synthetic utility of the current method on gram-scale reaction for several transformations. The C-B bonds of borylatedproducts could be converted to a variety of functionalities including C-O, C-C, C-C, C-Br, and C-Pbonds. Finally, we performed DFT calculations of desymmetrization to understand its reaction pathways.