Boron-Assisted Cobalt-Catalyzed C-H Methylation Using CO 2 and H 2 .

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 CO 2 /H 2 as a methylation reagent for selective C-H methylation of indoles and pyrroles in the presence of cobalt/B(C 6 F 5 ) 3 cocatalysts. The Lewis acidic additive B(C 6 F 5 ) 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 CO 2 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.