Metal-free hydrogen transfer reduction of 3-hydroxy-3-indolyloxindoles: a novel method for the synthesis of 3,3′-biindolin-2-onesElectronic supplementary information (ESI) available. See DOI: 10.1039/c8nj01621f

Herein, a new approach for the synthesis of 3,3′-biindolin-2-ones is reported. The transformation has been successfully performed following a one-step strategy starting from 3-hydroxy-3-indolyloxindoles. The reaction proceeds smoothly under mild conditions and is applicable to a broad scope of substrates. In this process, a number of products were obtained in good to excellent yields (≥99%) using Brønsted acid as a catalyst and benzothiazolines as the hydrogen source. A new approach for the synthesis of 3,3′-biindolin-2-ones has been successfully performed with high yield following a one-step strategy starting from 3-hydroxy-3-indolyloxindoles.