An Intramolecular Cycloaddition Approach to Construct Polysubstituted Pyrrolidones from Alkynyl Carboxamides and PTSA

An efficient synthetic route to highly substituted pyrrolidone derivatives has been developed from an easily available alkynyl carboxamide and 4-methylbenzenesulfonic acid (PTSA). In the reaction, PTSA is not only used as acid catalyst but also as a reactant to provide a source for OTs group. A mechanism is proposed to involve the protonation of the alcohol substrate/cyclopropylcarbinol-homoallylic rearrangement/intramolecular N-nucleophilic cyclization reactions.