Palladium-Catalyzed Regioselective B(9)-Amination of <i>o</i>-Carboranes and <i>m</i>-Carboranes in HFIP with Broad Nitrogen Sources
Yan‐Na Ma, Yan-Na Ma, Yan Gao, Yubin Ma, Yubin Ma, Yan Wang, Huazhan Ren, Xuenian Chen
Abstract
Amination of carboranes has a good application prospect in organic and pharmaceutical synthesis. However, the current methods used for this transformation suffer from limitations. Herein, we report a practical method for a highly regioselective formation of a B–N bond by Pd(II)-catalyzed B(9)-H amination of o- and m-carboranes in hexafluoroisopropanol (HFIP) with different nitrogen sources under air atmosphere. The silver salt and HFIP solvent play critical roles in the present protocol. The mechanistic study reveals that the silver salt acts as a Lewis acid to promote the electrophilic palladation step by forming a heterobimetallic active catalyst PdAg(OAc)3; the strong hydrogen-bond-donating ability and low nucleophilicity of HFIP enhance the electrophilic ability of Pd(II). It is believed that these N-containing carboranes are potentially of great importance in the synthesis of new pharmaceuticals.