A reaction route of natural indigoids

Abstract

Natural indigo is obtained by an empirical and traditional method, and the corresponding theoretical part is too brief: air oxidation of indoxyl in alkaline medium. The efforts were directed to the synthesis of the dye. However, the formation of indigo blue and its companion, indigo red (indirubin), is much more complex and deserves attention since there are involved interesting reactions. In this communication we provide the reaction series occurring in this process, giving the electron flow, step by step.