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.