Fischer Indole Synthesis in Low Melting Mixtures

Functionalized indoles are synthezised under mild conditions in a tartaric acid–dimethylurea melt. The melt serves as the solvent and as the catalyst. Under these reaction conditions, sensitive functional groups such as <i>N</i>-Boc, <i>N</i>-Cbz, or azides are stable, and indolenines are obtained regioselectively in excellent yields. The practical use of the method is demonstrated in the synthesis of the hormone melatonin.