[3 + 2] Annulation of Donor–Acceptor Cyclopropanes with Ammonium Thiocyanate: Interrupted Cascade Leads to Elusive Iminodihydrothiophene Derivatives

A zinc iodide-mediated [3 + 2] cyclization between donor–acceptor cyclopropanes and ammonium thiocyanate has been developed to afford 2-imino-tetrahydrothiophene derivatives under mild conditions. Subsequent transformation of these intermediates into 2-amino-dihydrothiophenes was achieved using neutral alumina as a Lewis acid. Unlike most of the previous methods that directly yield 2-amino-dihydrothiophenes, this approach enables selective access to unsubstituted 2-imino-tetrahydrothiophenes─a challenging target that is not widely accessible. This metal-mediated protocol is operationally simple, cost-effective, and environmentally benign. The synthetic utility of the products was demonstrated through a series of transformations, and a plausible reaction mechanism is proposed.