3-Alkyl-2-pyridyl Directing Group-Enabled C2 Selective C–H Silylation of Indoles and Pyrroles via an Iridium Catalyst

Abstract

An iridium-catalyzed, directing group-enabled site selective intra- and intermolecular silylation of indoles and pyrroles with hydrosilanes has been developed under ligand-free conditions. Fine-tuning of the removable 3-alkyl-2-pyridyl directing group was found to be crucial for achieving high yields for C2-silylated indole and pyrrole products. Moreover, the scalability was demonstrated, and further transformations of the silylation products were achieved.

C–H Bond Silylation of Heteroarenes

“…Template for SYNTHESIS Thieme In 2022, the Yang group reported a ligand free directed C2selective intra-and intermolecular C−H silylation strategy for indoles and pyrroles (25) via iridium catalysis (Scheme 8). 19 In this study, the directing group ( This article is protected by copyright. All rights reserved.…”

“…In 2022, the Yang group reported a ligand-free directed C2-selective intra-and intermolecular C-H silylation strategy for indoles and pyrroles 25 via iridium catalysis (Scheme 8). 19 In this study, the directing group (3-alkyl-2-pyridyl) plays a crucial role in controlling the regioselectivity. From several control experiments, reversibility of the C-H cleavage steps was observed, and it was therefore concluded that Si-H bond cleavage instead of C-H bond cleavage at the C2 position of indole might be involved in the rate-limiting step in this reaction.…”

Iridium(i) complexes with bidentate NHC ligands as catalysts for dehydrogenative directed C–H silylation

“…Taken together, these results support the reversibility of the ortho C-H bond cleavage step and suggest that the Si-H bond breaking, and not the C-H bond, is involved in the rate-determining step. 20,21 Finally, the catalytic silylation of substrate 3a conducted in the presence of access butylated hydroxytoluene (BHT), TEMPO [2,2,6,6-tetramethylpiperidine-1-oxyl], or mercury metal proceeded without noticeable decrease of activities (Fig. S11 and S12, ESI †), implying This journal is © The Royal Society of Chemistry 2023 that both the involvement of free radical processes or heterogeneous catalysis are unlikely to be operative.…”