Halocyclohexanes

Haloadamantanes are halocyclohexanes that have even lower reactivity toward nucleophiles than 1-haloadamantanes or the simple halocyclohexanes. 

Addition of aryl tellurium trihalides to cyclohexene produces trails-] -aryldihalotelluro-2-halocyclohexanes when the reactions are carried out in chloroform, and trans-1-aryldihalotelluro-2-methoxycyclohexanes when methanol is used as the reaction medium. Treatment of the 2-chlorocyclohexyl 4-methoxyphenyl tellurium dichloride with terf.-butyl hydroperoxide in acetic acid yielded tram-l,2-dichlorocyclohexane and aryl chloride. Bis[4-methoxyphenyl] tellurium dichloride did not yield any aryl chloride under these conditions1. Pyrolysis of tran.s-2-methoxycydohexyl phenyl tellurium dibromidc afforded Crum- l-bromo-2-methoxycyclohexane1. 

TABLE 10. Enthalpies (kJmol ) and IR Av(OH) frequency shifts (cm ) for the syn (17)-anti (18) isomerization of 2-halophenols and the intermolecular association of 4-fluorophenol with halocyclohexanes... 

Use of pyridinium iodide gave the corresponding iodides, but the proportion of 4-iodocy-clohexanone was lower. The analogous reactions of l-acetylbicyclo[3.1.0]hexane afforded good yields of trans- and cj5-l-acetyl-3-halocyclohexanes 6. 

The stable and selective inclusion of highly strained halocyclohexanes conformers or of monomeric carboxylic acids reveals the outstanding mutual fit of the TOT molecules constituting clathrate crystal, thus leading to a remarkable preservation of the cohesive van der Waals forces in the host lattice. But for a few exceptions, once formed the TOT clathrates prove to be thermally stable. 

The participation of the two mechanisms is indicated by the effect of added dimethyl sulfide. The presence of dimethyl sulfide suppressed formation of cyclohexanol, cyclohexanone and halocyclohexane but did not affect the production of r-butylperoxy-cyclohexane. In place of the former products, dimethyl sulfoxide was found. Since sulfides can act as a trap for a two-electron oxidant such as an iron-peroxo or an iron-oxo species, the formation of alcohol, ketone and haloalkane must involve heterolysis of the alkyl hydroperoxide, i.e. 

The hydroxylation of cyclohexane, adamantane and norcarane with PhIO and ClMnTPP leads mainly to the corresponding cycloalkanols [92]. A hydrogen abstraction mechanism is consistent with the product distribution pattern. A mixture of cyclohexanol and halocyclohexanes is obtained with other MnTPP complexes [93]. 

The required anti and coplanar transition state geometry can also be used to predict the regiochemistry of E2 elimination in halocyclohexanes such as chlorocyclohex-anes. In these molecules, anti and coplanar correspond to trans and diaxial. Consider the E2 reaction of the cis isomer of l-chloro-2-isopropylcyclohexane.The major product is 1-isopropylcyclohexene, the more substituted cycloalkene. 

For elimination reactions of halocyclohexanes, requiring axial C—H and C—X bonds, see Section 5.3.2.1... 

For elimination in halocyclohexanes both the C—H and C—X bonds must be axial. 

Nucleophilic attack on halocyclohexanes is also somewhat retarded compared with that on acyclic secondary haloalkanes, even though in this case bond-angle strain is not an important factor. Explain. (Hint Make a model, and refer to Chapter 4 and Section 6-10.)... 

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