Catalytic Access to Indole-Fused Benzosiloles by 2‑Fold Electrophilic C–H Silylation with Dihydrosilanes

A protocol for the
catalytic synthesis of indole-fused benzosiloles
starting from 2-aryl-substituted indoles and dihydrosilanes is reported.
Compared to known procedures, this method does not require prefunctionalized
starting materials and, hence, allows for a rapid access to those
siloles. The net reaction is a 2-fold electrophilic C–H silylation
catalyzed by cationic Ru–S complexes. Both reaction steps were
separately investigated, and these results eventually led to the development
of a two-step procedure. By preparing new Ru–S complexes with
different weakly coordinating anions (WCAs), it is also shown that
the latter can have a dramatic influence on the outcome of these reactions.
Furthermore, the substrate scope of the new method is discussed.