NIS-Promoted Chemodivergent and Diastereoselective Synthesis of Pyrrolinyl and Cyclopentenyl Spiropyrazolones via Regulated Cyclization of Alkylidene Pyrazolones with Enamino Esters.

An N-iodosuccinimide-promoted annulation of alkylidene pyrazolones with enamino esters has been explored to construct a spiropyrazolone moiety through a Michael addition/iodination/intramolecular nucleophilic substitution sequence. When the reaction was performed in acetonitrile at 100 °C, it furnished pyrrolinyl spiropyrazolones exclusively in an anti configuration through N-attacking cyclization. When the reaction was performed in dimethyl sulfoxide at 80 °C in the presence of K2HPO4, it afforded cyclopentenyl spiropyrazolones exclusively in the syn configuration through C-attacking cyclization. A plausible mechanism has also been proposed.

Regiodivergent Synthesis of 4,5'- and 4,4'-Imidazolinyl Spiropyrazolones from 4-Alkylidene Pyrazolones and Amidines.

The solvent-free reaction of 4-alkylidene pyrazolones with amidines can furnish 4,5'-imidazolinyl spiropyrazolones in good to excellent yields when promoted by N-iodosuccinimide under solvent-free ball-milling conditions, whereas it almost exclusively affords 4,4'-imidazolinyl spiropyrazolones if mediated by N-bromosuccinimide in heated toluene. On the basis of this switchable cyclization strategy, a powerful metal-free method for regioselective and diastereoselective synthesis of structurally diverse 4,5'- and 4,4'-imidazolinyl spiropyrazolones has been successfully developed.