FeCl3/TBHP-Mediated Oxidation of Indoles: Divergent Product Selectivity under Mechanochemical and Solution-Based Conditions

A condition-controlled diversity-oriented approach to access different frameworks by the FeCl₃/TBHP-mediated oxidation of indoles is developed. Oxidation of indoles produced 2-(indol-3-yl)indolin-3-ones in moderate to high (46-87%) yields under mechanochemical ball milling and benzoxazinones in good to excellent yields (9-90%) under solution-based conditions. The developed methods demonstrated a broad substrate scope and could be performed on a gram scale without compromising yield. Further, the mechanochemical approach avoids the use of traditional solvents and provides a green route for accessing 2-(indol-3-yl)indolin-3-ones under ambient conditions. The practical utility of the mechanochemical protocol has been demonstrated by synthesizing the naturally occurring bioactive compound 'Metagenediindole' in one step.