Development of a Practical One-Pot Synthesis of Indigo from Indole

Abstract A novel and highly practical one-pot synthesis of indigo from indole via 3-position selective oxidation and dimerization of the indole framework was developed. Using 0.1 mol % of molybdenum complex and 2.2 equivalents of cumene hydroperoxide in tert-butyl alcohol, the reaction was complete in 7 h and pure indigo was obtained in 81% yield as a deep-blue solid just by filtration. The described one-step method renders the pure indigo readily available on a large scale using only inexpensive raw materials.