Ultrasound-Activated Atom-Economical Approach to the Synthesis of Highly Substituted Pyrrolidin-2-ones through a Four-Component Ugi/5-endo-trig Intramolecular Radical Cyclization Reaction

Abstract

An efficient and diversity-oriented access to functionalized pyrrolidin-2-ones through an Ugi reaction of readily available starting materials with a subsequent transformation is described. A two-step reaction sequence of a four-component Ugi reaction and an intramolecular radical-cyclization reaction leads to the chemo- and regioselective formation of a single product with high atom economy and good to high yields. The radicalization of the pseudopeptides generated from the first step by a cavitational mechanism produces the key intermediate for the ultrasound-activated formation of γ-lactams as the final products by β-Michael addition. Among the advantages of this approach are its use of cavitation bubble implosion as an exclusive path to radicalization of the polyfunctional Ugi adduct, its high selectivity, and its short reaction times.