Facile Synthesis of Polysubstituted Spiro‐Pyrazolone‐Pyrrolines via (1 + 4) Annulations of 4‐Halo Pyrazolones With 1‐Heterodienes
A facile and mild synthetic route to polysubstituted spiro‐pyrazolone–pyrrolidinones has been developed via a formal (1 + 4) cycloaddition between 4‐halopyrazolones and acyclic conjugated imines. The reactions proceed in high yields (up to 95%) with excellent regioselectivity, delivering the target spirocyclic compou...