Synthesis of fused polyhalogeno-7a-hydroxy-[1,2-a]indol-5-one derivatives

A series of novel fused polyhalogeno-7a-hydroxy-[1,2-a]indol-5-one derivatives has been synthesized with good yields based on the Nenitzescu reaction of heterocyclic ketene aminals (HKAs) with halogenated quinones without catalyst in acetone under room temperature. The highly efficient, catalyst-free and one pot synthesis serves as a nice addition to group-assisted-purification (GAP) chemistry, and the pure products were obtained simply by washing the crude products with 95% ethanol.