Highly Diastereoselective\nSynthesis of 2,3-Dihydropyrroles\nvia Formal [4 + 1] Annulation Reaction of α,β-Unsaturated\nImines and <i>in Situ</i> Generated Pyridinium Ylide

We report a cascade approach for\nthe synthesis of 2,3-dihydropyrroles\nderivatives via a formal [4 + 1] annulation reaction of α,β-unsaturated\nimines with <i>in situ</i> generated pyridinium ylides.\nImportantly, this protocol is compatible with diverse substituted\nimines as well as pyridinium ylides, constructing 2,3-dihydropyrroles\nwith excellent yield and selectivity. Thereafter, the Merrifield resin-supported\npyridinium ylide as a potential C1 synthon was also employed in our\nstrategy and reused several times, resulting in products with excellent\nyield and diastereoselectivity.