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 (E)-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.