Zur elektrocyclischen Ringöffnung von Cyclopropylhalogeniden bei der Reaktion mit Natriumiodid in Aceton / Electrocyclic Ring Opening of Cyclopropyl Halides in the Course of their Reaction with Sodium Iodide in Acetone

Abstract

Abstract Reaction of cyclopropyl halides with sodium iodide in acetone (i.e. under typical SN2-conditions), proceeds via ring opening to allylic systems finally yielding 1,5-hexadienes upon dimerisation; ring-retained products were not detected. Application of the Wood-ward-Hoffmann rules lends strong support to a cationic synchronous mechanism. This is also confirmed by kinetic measurements proving this reaction to be first order over all. The kinetic data are shown to fit the Hammett equation using σ-values for cyclopropyl bromides and σ+-values for geminal cyclopropyl dichlorides, respectively. The validity of the Woodward-Hoffmann-De Puyrule (according to which in synchronous reactions leaving groups situated endo are strongly favored over those situated exo) is tested in corresponding experiments involving condensed ring systems.