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Reactivities of Methylenetriangulanes and Spirocyclopropanated Bicyclopropylidenes toward Bromine. Relative Stabilities of
 

Summary: Reactivities of Methylenetriangulanes and Spirocyclopropanated
Bicyclopropylidenes toward Bromine. Relative Stabilities of
Spirocyclopropanated versus Methyl-Substituted Bromonium Ions
Sergei Kozhushkov, Thomas Spašth, Torsten Fiebig, Bernard Galland,
Marie-Francoise Ruasse,*, Prince Xavier,§ Yitzhak Apeloig,*,§ and Armin de Meijere*,
Institut fušr Organische Chemie der Georg-August-Universitašt Gošttingen, Tammannstrasse 2,
D-37077 Gošttingen, Germany, Institut de Topologie et de Dynamique des Syste`mes de l'UniversiteŽ Paris
7-Denis Diderot, associeŽ au CNRS, URA 34, 1 rue Guy de la Brosse, F-75005 Paris, France, and
Department of Chemistry and the Lise Meitner Minerva Center for Computational Quantum Chemistry,
TechnionsIsrael Institute of Technology, Technion City, 32000 Haifa, Israel
Armin.deMeijere@chemie.uni-goettingen.de
Received November 6, 2001
The bromine additions to methylenecyclopropane (1), bicyclopropylidene (2), and spirocyclopro-
panated methylenecyclopropanes and bicyclopropylidenes 3-6 in methanol at 25 °C proceed
essentially with the same rate as those to the corresponding oligomethyl-substituted ethylenes.
An increasing number of spiroannelated three-membered rings enhances the rate of bromination
and stabilizes the intermediate cyclopropyl bromonium cations against ring opening in the course
of bromine addition. Calculations at the B3LYP/6-311G(d,p) level show that unsymmetrical
bromonium ions are the intermediates, and that they are stabilized by the spiroannelation with
cyclopropane rings. The bromonium ion derived from 1 is less stable by 6.3 kcal mol-1

  

Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology

 

Collections: Chemistry