Zur elektrocyclischen Ringöffnung von Cyclopropylhalogeniden bei der Reaktion mit Natriumiodid in Aceton

R e i n e r L u c k e n b a c h u n d N i k o l a u s M ü l l e r [1] Organisch-Chemisches Institut der Universität Mainz Z . Naturforsch. 34b, 464 -480 (1979); eingegangen am 10. A u g u s t / 1 9 . Dezember 1978 R ing Opening, W o o d w a r d H o f f m a n n Rules, Allylic Cations, Dimerisation, 1,5-Hexadienes React ion of cyc lopropyl halides with sodium iodide in acetone [i.e. under typical Sis-2-conditions), proceeds via ring opening to allylic systems finally yielding 1,5-hexadienes upon dimerisation; ring-retained products were not detected. Appl icat ion of the W o o d w a r d H o f f m a n n rules lends strong support to a cationic synchronous mechanism. This is also confirmed b y kinetic measurements proving this reaction t o be first order over all. The kinetic data are shown to fit the Hammett equation using cr-values for cyc lopropy l bromides and o+-values for geminal cyc lopropyl dichlorides, respectively. The validity o f the W o o d w a r d H o f f m a n n D e 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.