Highly Diastereoselective Synthesis of 2,3-Dihydropyrroles via Formal [4 + 1] Annulation Reaction of α,β-Unsaturated Imines and in Situ Generated Pyridinium Ylide

We report a cascade approach for the synthesis of 2,3-dihydropyrroles derivatives via a formal [4 + 1] annulation reaction of α,β-unsaturated imines with in situ generated pyridinium ylides. Importantly, this protocol is compatible with diverse substituted imines as well as pyridinium ylides, constructing 2,3-dihydropyrroles with excellent yield and selectivity. Thereafter, the Merrifield resin-supported pyridinium ylide as a potential C1 synthon was also employed in our strategy and reused several times, resulting in products with excellent yield and diastereoselectivity.