Synthesis of Highly Functionalized Pyrrolidines via a Selective Iodide-Mediated Ring Expansion of Methylenecyclopropyl Amides

This manuscript describes a highly selective iodide-mediated, tandem Mannich/cyclization to afford trans-2,3-disubstituted pyrrolidines from methylenecyclopropyl amides in good to excellent yields and selectivities. The reaction scope has been drastically expanded to include a wide array of aromatic, heteroaromatic and alpha,beta-unsaturated imines, as well as a variety of methylenecyclopropyl amides. Additionally, mechanistic studies were carried out to ascertain the nature of the ring-opening/ring-closing mechanism using deuterated substrates. Results from these studies indicate that the primary mechanism is an S(N)2/S(N)2 ring opening/ring closing and that iodine- or iodide-mediated isomerization of the iodo enolate is likely occurring.