Fe(III)-Mediated Two-Fold Oxidative Coupling of Furan with Indole provides Modular Access to Bis(Indolyl)Furans - A New Class of Tetra-(hetero)arylated Furan with up to four different Substituents

Highly arylated heteroarenes constitute an intriguing class of molecular scaffolds for material science applications. Among these, tetraarylated furans have demonstrated differentiated properties as compared to other similar heterocyclic cores. Among tetraarylated furans, the synthetic complexity increases drastically with increasing number of different peripheral aryl groups. There are only a very limited number of methodologies developed to access furans with four different (hetero)aryl substituents, none of which involve oxidative coupling on furan core. Herein, we report the first methodology based on a sequential two-fold oxidative C-C coupling of furans with indoles to access bis(indolyl)furans - a new class of tetra-(hetero)arylated furans with up to four different substituents. Moreover, the reaction is mediated by inexpensive, earth-abundant FeCl3.6H2O and displays wide substrate scope and aqueous compatibility. Through the characterization of the photophysical and electrochemical properties of this novel class of furans, we present the first validation of the extensively studied aggregation-caused quenching (ACQ) property of tetraarylated furans beyond phenyls as peripheral groups.