Benzene chlorination strategy

T. Agapie, P. L. Diaconescu, and C. C Cummins, Methine (CH) Transfer via a Chlorine Atom Abstraction/Benzene-Elimination Strategy Molybdenum Methylidyne Synthesis and Elaboration to a Phosphaisocyanide Complex, Angew. Chem. Int. Ed. 45, 862-870 (2006). 

Phytoremediation was estimated to cost approximately 3500/kg of waste treated at a site contaminated with benzene, toluene, ethylbenzene, and xylene (BTEX) chlorinated solvents and other volatile organic compounds. Total savings associated with using phytoremediation at the site instead of conventional pump-and-treat strategies were estimated to be 13 million over the course of the project (D186678, p. 29). 

To substantiate this mechanism, haloquinolines (75) were used. The strategy was to hinder sterically the addition of superoxide. In the case of 6-chloroquinoline, the products were the same as those formed from quinoline, except that they were chlorinated, which was expected because position 6 is not involved in either mechanism. Halogen substitution on the pyridine moiety in part directed oxygen addition to the benzene moiety, which was consistent with superoxide addition onto the more accessible positions on the benzene ring of the halogenated radical cation. This result supports the fact that a cycloaddition mechanism can take place in the photocatalytic degradation of quinoline. This mechanism has been proposed in the case of other aromatics, such as 4-chlorophenol (76) and 4-chloro-catechol (77). 

Two different strategies have been developed for C-Cl activation with rhodium compounds (a) oxidative addition of C-Cl bonds to electron-rich Rh(I) complexes and (b) -coordination of coordinatively unsaturated, electron-deficient Rh(III) species with the benzene ring of ArCI, followed by aromatic nucleophilic substitution of chlorine in the thus activated aromatic system. 

A tandem polycyclization-Pinacol process has been developed using a similar strategy as described above. As shown in Scheme 29, the polyfunctionahzed phenol 100 is transformed into the compound 104 when treated with [bis(trifluoroacetoxy) iodo]benzene in a mixture of hexafluoroisopropanol and dichloromethane [25]. The reaction occurs through a succession of chair-Uke transition states, in which the phenoxenium ion 101 is first trapped by the endocychc alkene to deliver the intermediate 102, which then reacts with the alkyne to produce cation 103. The process concludes with a pinacol-like ring contraction. The presence of a chlorine... 

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