Switching of “Rollover Pathway” in Rhodium(III)-Catalyzed C–H Activation of Chelating Molecules

Organic molecules containing imidazolium
and pyridine backbone
are of special interest in many branches of chemistry, and therefore,
overcoming the scarcity of their catalytic functionalization protocol
leading to structurally important derivatives is strongly desired.
This study demonstrates an unprecedented bimodal C–H activation–functionalization
catalysis on such organic molecules which contain imidazolium motif
(potential N-heterocyclic carbene donor) and pyridine in chelating
fashion and difficult to functionalize by trivial C–H activation
strategy. The unique feature of this protocol is a flip-flop NHC-directed
pyridine rollover and pyridine-directed NHC-rollover C–H activation
within a stable “NHC–RhIII–pyridine”
chelate platform followed by functionalization with internal alkynes
to furnish structurally important annulated products. Electronic and
steric factors play a key role in achieving such novel chemistry.