Calcium-Catalyzed, Dehydrative, Ring-Opening Cyclizations of Cyclopropyl Carbinols Derived from Donor–Acceptor Cyclopropanes

A calcium-catalyzed, dehydrative, ring-opening cyclization of (hetero)­aryl cyclopropyl carbinols is reported. The cyclopropyl carbinols are prepared directly from the corresponding donor–acceptor (D–A) cyclopropanes. The calcium catalyst catalyzes the formation of putative (hetero)­aryl cyclopropyl carbinyl cations that undergo ring-opening to allylcarbinyl cations. Subsequent intramolecular Friedel–Crafts reaction affords (hetero)­aryl-fused cyclohexa-1,3-dienes in up to 97% yield. This approach represents the first example of catalysis for this intramolecular, dehydrative ring-opening cyclization and outperforms the previous reports using stoichiometric Lewis acids