Boron-Assisted Cobalt-Catalyzed C-H Methylation Using CO2 and H2

C-H methylation of heteroarenes (e.g., indoles, pyrroles, etc.) is frequently applied in the synthesis of drug/biorelated compounds. We herein report the use of CO2/H-2 as a methylation reagent for selective C-H methylation of indoles and pyrroles in the presence of cobalt/B(C6F5)(3) cocatalysts. The Lewis acidic additive B(C6F5)(3) is essential to achieving good reactivity for a broad scope of substituted indoles and pyrroles (20 examples, up to 92% yields). The C-H methylation is accomplished via the CO2 reduction/C-C bond formation/reduction sequence. Water is the only byproduct. This system based on the use of non-noble metal catalysts features an environmentally benign alternative for C-H methylation.

Automated summary

In this study, CO2/H2 was used as a methylation reagent for selective C-H methylation of heteroarenes. The reaction was catalyzed by cobalt/B(C6F5)3, and the Lewis acidic additive B(C6F5)3 played a crucial role in achieving good reactivity. The reaction proceeds via CO2 reduction, C-C bond formation, and reduction. Water is the only byproduct of this environmentally friendly alternative for C-H methylation.