2-bromocyclohexyl

A preliminary indication that bromonium ions could be formed reversibly was provided by the reaction of adamantylideneadamantane (p. 249) leading to a highly stable bromonium-tribromide ion pair that readily releases bromine and the initial alkene (Strating et al, 1969). However, the first evidence for possible return came from the acetolysis of 2-bromocyclohexyl-brosylate in the presence of bromide ions. It was shown (Brown et al, 1984) that the cyclohexylbromonium ion intermediate is able to release bromine. The drastic reaction conditions (high temperature, long duration and high bromide concentrations) cast some doubt on the generality of this observation. 

Hydroperoxy acetals l-Hydroxy-2-bromocyclohexyl hydroperoxide (28) (XAHPOL) 1.473 1.423 104.4 99... 

Figure 10. Correlation of solvolytic rate constants for trans-2-bromocyclohexyl p-bromobenzenesulphonate [43] at 50° and Y (data from Winstein et al., 1951).

Another aspect of the mechanism is the reversibility of formation of the bromonium ion. Reversibility has been demonstrated for highly hindered alkenes, and attributed to a relatively slow rate of nucleophilic capture. However, even the bromonium ion from cyclohexene appears to be able to release Br2 on reaction with Br. The bromonium ion can be generated by neighboring-group participation by solvolysis of frfln -2-bromocyclohexyl triflate. If cyclopentene, which is more reactive than cyclohexene, is included in the reaction mixture, bromination products from cyclopentene are formed. This indicates that free Br2 is generated by reversal of bromonium ion formation. Other examples of reversible bromonium ion formation have been found. " ... 

A slow stream of nitrosyl diloride bubbled at room temp, through a soln. of methyl l-methoxy-2-bromocyclohexyl ketoxime in CCI4, the gas stream stopped after the soln. has become dark brown, and allowed to stand 10 min. methyl l-methoxy-2-bromocyclohexyl nitroketimine. Y 89%. - Similarly Methyl 1,2-di-... 

A soln. of bromide in benzene added dropwise to a vigorously stirred suspension of finely powdered silver monofluoride and cyclohexene in benzene or acetonitrile frans-2-bromocyclohexyl fluoride. Y 80%. F. e. s. L. D. Hall,... 

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