Cyclopentene Synthesis by a Catalytic [3+2] Annulation of Donor‐Acceptor Cyclopropanes with Polarized Alkenes

[3+2] Annulation of donor‐acceptor cyclopropanes with alkynes represents an efficient route to cyclopentenes. Here, we describe a new cyclopentene synthesis via Lewis acid‐catalyzed ring‐opening addition and intramolecular S N V reaction of donor‐acceptor cyclopropanes with alkenes. The reaction is carried out under the catalysis of Sc(OTf) 3 by using polarized alkenes, namely α‐oxo ketene dithioacetals, as 2 C...