Indoxyl-based umpolung strategy for the synthesis of unsymmetrical 3,3′-biindoles

3,3′-Bisindoles are known to be important structural motifs found in bioactive natural products, pharmaceuticals, and functional materials. Herein, a novel indoxyl-based approach was established for the synthesis of unsymmetrical 3,3′-biindoles from indoles and indoxyls. This approach generated moderate to excellent yields of the desired products (24 examples, up to 98% yield). The present method features broad substrate scope, operational simplicity, high atom economy, and utilization of non-toxic and inexpensive molecular iodine as catalyst. The applicability of this method has been demonstrated by the facile gram-scale synthesis.