Direct synthesis of pillar[5]quinone and pillar[6]quinone by CAN oxidation of alkylated pillararenes

Abstract

We report a simple and efficient high-yielding synthesis of pillar[n]quinones (n = 5 and 6) by direct oxidation of alkoxy pillararenes, using ceric ammonium nitrate (CAN) in aqueous acetonitrile. Avoiding halogenated solvents, dimethoxy pillar[5]arene was transformed to pillar[5]quinone (92% yield) and diethoxy pillar[6]arene to pillar[6]quinone (90% yield) in 30 min. A broad substrate scope allows direct oxidation of most alkoxy pillararenes, accessible through a Lewis acid catalyzed direct synthesis, and make pillarquinones readily available for future exploration of reactivity and host-guest properties.