Phosphorus(III)-assisted regioselective C-H silylation of heteroarenes

Heteroarenes containing carbon-silicon (C-Si) bonds are important building blocks that play an important role in the construction of natural products, pharmaceuticals, and organic materials. In this context, the C-H silylation of heteroarenes is a topic of intense interest. Indole C-H silylation can preferentially occur at the nucleophilic C3 and C2 position (pyrrole core), while accessing the C4-C7 positions (benzene core) of the indole remains highly challenging. Here, we show a general strategy for the regioselective C7-H silylation of indole derivatives. Mainly, the regioselectivity is determined by strong coordination of the palladium catalyst with phosphorus (III) directing group. Using this expedient synthetic strategy, the diverse C7-silylated indoles are synthesized effectively which exhibits the broad functional group compatibility. Moreover, this protocol also been extended to other heteroarenes such as carbazoles. The obtained silylated indoles have been employed in various transformations to enable the corresponding differently functionalized indole derivatives. Significantly, a cyclopalladated intermediate is successfully synthesized to test the hypothesis about the P(III)-directed C-H metalation event. A series of mechanistic experiments and density functional theory (M06-2X) calculations has shown the preferred pathway of this directed C-H silylation process. Indole C-H silylation preferentially occurs at the C3 and C2 positions, while functionalization of the benzene core (C4-C7 sites) remains challenging. Here, the authors report a regioselective C7-H silylation of indole derivatives assisted by strong coordination of the palladium catalyst with a phosphorus directing group.

Automated summary

This study presents a regioselective C7-H silylation of indole derivatives assisted by strong coordination of the palladium catalyst with a phosphorus directing group. The method allows for the effective synthesis of various C7-silylated indoles with broad functional group compatibility. Additionally, the hypothesis regarding the P(III)-directed C-H metalation event is successfully tested through mechanistic experiments and DFT calculations.