Microwave-assisted synthesis of 4,6-disubstituted isoindoline-1,3-diones by Diels-Alder reactions

Abstract

The synthesis of 4,6-disubstituted isoindoline-1,3-diones through microwave-assisted Diels-Alder (DA) reactions is reported. Chromones bearing an α,β-unsaturated carbonyl system at C-3 were used as dienes and a scope of maleimides as dienophiles was investigated. The proposed mechanism involves a DA reaction of 3-benzoylvinylchromones with different maleimides, followed by chromanone ring opening and in situ oxidation. The observed aromatization of DA adducts was accomplished without employment of any oxidizing agent and can be explained by the presence of several acidic protons due to the electron-withdrawing groups (carbonyl groups), affording the 4,6-disubstituted isoindoline-1,3-diones in 15-59% yield. Among tested maleimides, N-phenylmaleimide revealed to be the most reactive dienophile, yielding the corresponding 2-phenylisoindoline-1,3-dione in 59% yield.