Cyclohexenes bromination

Bienvenue et al. (1980). Bellucci et al. (1985a). cIn kcal mol relative to MeCN. Rate constant of cyclohexene bromination at 25°C. 

Cyclohexene, bromination of, 47, 32 reaction with 1-butyl perbenzoate and cuprous bromide, 48,18 2-Cyclohexenol, 46, 32 2-Cyclohexen-I-ol, benzoate, 48, 18 2-Cyclohexenone, 45, 32 Cydohexyl allophanamide, 45, 72 Cyclohexylamine, 45, 85 reaction with 1-butyl hypochlorite, 46, 16... 

The rate of cyclohexene bromination, too (in carbon tetrachloride), is lowered by the presence of NBS (or of other hydrogen bromide scavengers)74,102 probably, the reaction is complicated by the presence of further complexes, such as the tribromide of the cyclohexene bromonium ion. 

In the two examples cited so far the chlorination of propene and the bromination of cyclohexene both criteria are met... 

Thermal decomposition gives olefins, probably by rearrangement of intermediate carbenes. For example, the decomposition of 3,3-penta-methylenediazirine (68) in nitrobenzene above 160°C gives cyclohexene [Eq, (58)]. The yield as determined by bromine titration... 

Another method for preparing alkyl halides from alkenes is by reaction with jV-brotnosuccinimide (abbreviated NBS) in the presence of light to give products resulting from substitution of hydrogen by bromine at the allylic position—the position next to the double bond. Cyclohexene, for example, gives 3-bromo-cyclohexene. 

The products of allylic bromination reactions are useful for conversion into dienes by dehydrohalogenation with base. Cyclohexene can be converted into 1,3-cyclohexadiene, for example. 

The 1,2-dibromocyclohcxane was prepared by the method of Snyder and Brooks 2 If the cyclohexene is cooled to ca —30° with a dry ice-isopropyl alcohol bath and the bromine is not diluted, it is possible to run this preparation on a threefold scale in one-third of the recorded time The product was always purified by the recommended procedure. 

Table 1 Formation Constants and Molar Absorptivities at 287 nm of the 1 1 Cyclohexene-Br2 CTC Obtained from Initial Absorbances of Mixtures of Bromine and Cyclohexene in 1,2-Dichloroethane...

Table 2 Third-order Rate Constants for the Bromination of Cyclohexene in 1,2-Dichloroethane a... 

Enantioselective bromination of cyclohexene (11) in an inclusion complex with the optically active host compound, (i, i )-(-)-trans-4,5-bis(hydroxy-diphenylmethyl)-2,2-dimethyl-l,3-dioxacyclopentane (10a) was accomplished. 

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