The reduction of unprotected indoles and quinolines is described using water as a hydrogen source. The method is based on the application of a RANEY® type Ni–Al alloy in an aqueous medium. During the reaction the Al content of the alloy, used as reductants, reacts with water in situ providing hydrogen and a RANEY® Ni catalyst, thus the alloy serves as a hydrogen generator as well as a hydrogenation catalyst. The simplicity and efficacy of the method are illustrated by the selective reduction of a variety of substituted indoles and quinolines to indolines and tetrahydroquinolines, respectively.
Organic & Biomolecular Chemistry
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