An X⁻ (X = I, Br)-Triggered Ring-Opening Cyclization of Cyclopropenyl-Substituted Alkyl Halides or Mesylates: An Efficient and Highly Regio- and Stereoselective Approach to (<i>E)</i>-Haloalkylidene 4−7-Membered Cyclic Compounds

Polyfunctionalized (E)-haloalkylidene cyclic products were efficiently synthesized in moderate to excellent yields via a regio- and stereoselective X− (X = I or Br)-triggered ring-opening intramolecular trapping of cyclopropenes 1. The reaction can be used for construction of 4−7-membered products. The E-stereoselectivity of the exo-CC bond is very high. The carbon−halogen bond in the exo-CC bond may further be elaborated to prepare differently substituted cyclic products with a stereodefined CC bond.