Metal‐Free Transfer C−H Borylation of Substituted Thiophenes

Abstract

AbstractThiophenes are crucial chemical building blocks in the fields of medicinal and material chemistry. As such, the C−H functionalization of these units is of key importance for developing novel applications. Herein, we report the C−H borylation of thiophenes using metal‐free transfer C−H borylation. When performed on C2‐substituted thiophenes, the reaction is selective for the borylation on C5, while C3‐substituted thiophenes are borylated on C2, a complementary selectivity from reported C−H borylation approaches that typically prefer to borylate at the C5 position. An optimization of the catalytic system was performed. The reaction was shown to work with electronically diverse thiophenes and was also compatible with sensitive functional groups. Computational investigation of the reaction mechanism suggests a Lewis pair C−H activation mechanism with a selectivity that is kinetically driven. The methodology developed herein is an economical pathway for the preparation of C2‐borylated C3‐substituted thiophenes.