33742-80-2Relevant articles and documents
Reactivities of methylenetriangulanes and spirocyclopropanated bicyclopropylidenes toward bromine. Relative stabilities of spirocyclopropanated versus methyl-substituted bromonium ions
Kozhushkov, Sergei,Spaeth, Thomas,Fiebig, Torsten,Galland, Bernard,Ruasse, Marie-Francoise,Xavier, Prince,Apeloig, Yitzhak,De Meijere, Armin
, p. 4100 - 4114 (2002)
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 than that from isobutene. One or two spirocyclopropane rings as in 3 and 4 stabilize the corresponding bromonium ion by 9.6 and 16.4 kcal mol-1, respectively, while one or two α-cyclopropyl substituents as in ethenylcyclopropane (7) and 1,1-dicyclopropylethene (8) stabilize the corresponding bromonium ions by 13 and 29 kcal mol-1, respectively. The experimental bromination rates of all the studied alkenes correlate reasonably well (r2 = 0.93) with calculated relative energies of the corresponding bromonium ions. The correlation is even better within the series of methylenecyclopropanes 1, 3, and 4 (r2 = 0.974) and bicyclopropylidenes 2, 5, and 6 (r2 = 0.999). The experimental bromination rates also correlate fairly well with the first ionization energies of the corresponding alkenes 1-12 (with r2 = 0.963) and 13-19 (with r2 = 0.991). The calculated preferred nucleophilic attack of a water molecule at both the C1′ and C1 atoms of representative bromonium ions conforms well to the experimentally observed product distribution.
The effect of strain on reactivity: Poor leaving groups increase strain-induced inhibition of alkene-forming elimination
Volta, Luca,Stirling, Charles J. M.
, p. 2481 - 2482 (2007/10/03)
Elimination to form a carbon-carbon double bond exocyclic to a cyclopropane ring is inhibited by factors which increase from 1.4 to 104.5 as the leaving group becomes poorer; strain induced in the transition structure can amount to some 50% of
