Brønsted Acid-Promoted Formation of Stabilized Silylium Ions for Catalytic Friedel–Crafts C–H Silylation

A counterintuitive approach to electrophilic
aromatic substitution
with silicon electrophiles is disclosed. A strong Brønsted acid
that would usually promote the reverse reaction, i.e., protodesilylation,
was found to initiate the C–H silylation of electron-rich (hetero)­arenes
with hydrosilanes. Protonation of the hydrosilane followed by liberation
of dihydrogen is key to success, fulfilling two purposes: to generate
the stabilized silylium ion and to remove the proton released from
the Wheland intermediate.