Synthesis of 2‑Unsubstituted Pyrrolidines and Piperidines from Donor–Acceptor Cyclopropanes and Cyclobutanes: 1,3,5-Triazinanes as Surrogates for Formylimines

A synthetic procedure to access 2-unsubstituted pyrrolidines and piperidines is presented. In the presence of MgI₂ as Lewis acid, donor–acceptor cyclopropanes or corresponding cyclobutanes were treated with 1,3,5-triazinanes, leading to the five- or six-membered ring systems under mild conditions in yields up to 93%. This protocol tolerates a great variety of functional groups and thus provides an efficient entry to this class of pyrrolidines and piperidines.