Efficient Utilization of Tetrabutylammonium Bifluoride in Halofluorination Reactions
The halofluorination reaction of a variety of alkenes by using tetrabutylammonium bifluoride (TBABF) in the presence of N-halosuccinimide is described.This process occurs stereospecifically to afford anti addition products, and with unsymmetrical olefins a marked Markovnikov-type regioselectivity is observed.In some cases, formation of a remarkable amount of the corresponding dihalo derivatives was found, but this undesirable side reaction can be avoided by using N-iodosucciniumide (NIS) as halogenating agent.If N-bromosuccinimide (NBS) or N-chlorosuccinimide (NCS) is utilized, these dihalo compounds can be easily removed from the halofluorinated compounds by simple column chromatography on silica gel.A mechanism for this side reaction is postulated.
Camps, F.,Chamorro, E.,Gasol, V.,Guerrero, A.
p. 4294 - 4298
(2007/10/02)
MECHANISMS OF FREE-RADICAL REACTIONS. XX. REACTIVITY IN THE FREE-RADICAL HALOGENATION REACTIONS OF ARYLFLUOROALKANES
The free-radical chlorination and bromination of meta- and para-substituted benzyl fluorides and 1,1-difluoro-2-phenylethane and also the chlorination of 1-fluoro-2-arylethanes by phenylchloroiodonium chloride and the bromination of meta- and para-substituted benzyl bromides were studied by the method of competing reactions.In all cases a good correlation is observed between log krel and the Brown ?+ constants.In cases where change in the reactivity in the transition from one reaction series to another is due mainly to the polar effect of the substituent whilethe selectivity is measured in relation to the polar effect direct relationships are observed between the reactivity and the selectivity.
Dneprovskii, A. S.,Eliseenkov, E. V.
p. 711 - 719
(2007/10/02)
MECHANISMS OF FREE-RADICAL REACTIONS. XIII. MECHANISM AND SELECTIVITY OF THE FREE-RADICAL HALOGENATION OF ALKYL AROMATIC HYDROCARBONS WITH FLUOROALKYL SUBSTITUENTS
The free-radical chlorination and bromination of 1-fluoro-2-arylethanes and 1,1,1-trifluoro-2-arylethanes was studied by the method of competing reactions.In all cases a good correalation between log krel and the Brown ?+ constants was observed.The variation of the selectivity in the transition from one reaction series to the other indicates that two independent factors which determine the reactivity (the change in the dissociation energy of the C-H bond and the polar effect of the substituents) have a simultaneous effect.
Dneprovskii, A. S.,Eliseenkov, E. V.,Mil'tsov, S. A.
p. 317 - 324
(2007/10/02)
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