Catalyst-Free "On-Water" Regio- and Stereospecific Ring-Opening of Spiroaziridine Oxindole: Enantiopure Synthesis of Unsymmetrical 3,3'-Bisindoles.

A catalyst-free water-mediated regio- and stereospecific ring-opening reaction of nonracemic spiroaziridine oxindoles and indoles has been developed with retention of configuration. This method provides direct access to enantiopure 3,3'-mixed bisindoles with excellent yield and enantioselectivity (up to 98% ee).