Iron(III)‐Catalyzed Cycloisomerizations of Acetal–Vinylidenecyclopropanes: An Efficient Synthetic Route to 1,2‐Disubstituted Cyclobutenes

A novel iron(III)-catalyzed intramolecular cycloisomerization of acetal-vinylidenecyclopropanes to afford a series of halogenated 1,2-disubstituted cyclobutenes tethered with a tetrahydropyrrole has been developed. The reaction is thought to proceed through a formal iron-catalyzed Prins cyclization followed by a ring-enlarging rearrangement of the methylenecyclopropane carbocation. The present protocol provides an alternative route to functionalized disubstituted cyclobutenes and the corresponding products could be successfully transformed into eight-membered oxacyclic products.