A Green Aerobic Oxidative Synthesis of Pyrrolo[1,2-<i>a</i>]quinoxalines from Simple Alcohols without Metals and Additives

Abstract

A practical and concise protocol for the efficient preparation of pyrrolo[1,2-a]quinoxalines through a cascade of alcohol oxidation/imine formation/intramolecular cyclization/oxidative dehydrogenation has been established. A series of substituted pyrrolo[1,2-a]quinoxaline derivatives were constructed readily in yields of 53-93% from the cheap primary alcohols by using dioxygen as the terminal oxidant. Remarkably, the fact that no extra metals and additives were necessary makes this unprecedented aerobic oxidation process highly step- and atom-economical. The usefulness of this transformation was further demonstrated with the gram-scale synthesis of compound 3aa under standard conditions.