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Reactions of Cyclohexenyl Iodonium Tetrafluoroborate with Bromide Ion: Retardation Due to the Formation of λ 3 -Bromoiodane

2006; American Chemical Society; Volume: 71; Issue: 4 Linguagem: Inglês

10.1021/jo0523013

1520-6904

Tadashi Okuyama, Shohei Imamura, Morifumi Fujita,

Nitric Oxide and Endothelin Effects

The reaction of 4-tert-butylcyclohex-1-enyl(phenyl)iodonium tetrafluoroborate (1a) and the 4-chlorophenyl derivative (1b) with bromide ion was examined in methanol, acetonitrile, and chloroform. Products include those derived from the intermediate cyclohexenyl cation as well as 1-bromocyclohexene. Kinetic measurements show that the reaction of 1 is strongly retarded by the added bromide. The curved dependence of the observed rate constant on the bromide concentration is typical of a pre-equilibrium formation of the intermediate adduct with a fast bromide-independent reaction (solvolysis of the iodonium ion). The formation of the adduct, lambda3-bromoiodane, was also confirmed by the UV spectral change. The relative reactivity of the iodonium ion and lambda3-bromoiodane is evaluated to be on the order of 10(2). The bromide substitution product forms both via the S(N)1 reaction of the free iodonium ion and via the ligand coupling of the iodane.