Pd-Catalyzed Sequential Arylation of 7-Azaindoles: Aggregate-Induced Emission of Tetra-Aryl 7-Azaindoles.

Pd-catalyzed synthesis of multi-aryl 7-azaindoles using sequential arylation of 5-bromo-6-chloro-3-iodo-1-methyl-1H-pyrrolo[2,3-b] pyridine is established. Four diverse aryl groups are installed in a chemo-selective fashion providing a general method to synthesize sterically encumbered compounds and extended 7-azaindoles in 48-95% yields. Three-selective sequential arylations at C-3, C-5, and C-6 via Suzuki-Miyaura cross-coupling followed by direct C-2 arylation using a Pd catalyst and AgOTf as an additive are highlights of the present work. Interestingly, the tetra-aryl 7-azaindoles showed aggregate-induced emission (AIE) making it potentially useful as fluorophores in OLEDs, sensors, and bio-imaging tools.