Cydohexyl radicals

Hoffmann, R. Ruckert, T. Bruckner, R. [1,2]-Wittig rearrangement of a lifhioalkyl benzyl ether with inversion of configuration at the carbanion C atom. Diastereoselective reductions of cydohexyl radicals with Li arerie. Tetrahedron Lett. 1993, 34, 297-300. 

Many companies have studied the optimization of catalyst composition and process conditions in order to improve the performance of the reaction and the economics ofthe process. In the Gulf process, the reaction is carried out at 90-100 °C, with a Co(III) acetate catalyst and acetic acid as the solvent [17]. The molar selectivity is around 70-75%, for a cyclohexane conversion that can be as high as 80-85%. The high concentration of Co(III) acetate used also favors the direct reaction ofthe cation with cyclohexane, generating the cydohexyl radical. In fact, in Gulf patents the reaction is reported to occur in a critical amount of Co(III) (25-150 mmoles per mole of cyclohexane). The catalyst is activated during the initial induction period, and water is also added in the initial stage to enhance the selectivity to AA, but the rate of production decreases because the induction period increases. 

Factors that influence the ground state conformation of 1 are also important in the transition state for addition of a radical at the carbon bearing the carboxamide. For I, the proximal methyl of the pyrrolidine protects the back face of the alkene, and addition occurs predominantly from the front, or Si, face. Figure 2 shows the relative rates of addition of cyclohexyl radical to 1 and 2 at 22 C [9]. The proximal methyl group on 1 reduces the rate of cydohexyl radical addition to the Re face of the alkene by a factor of 20 at room temperature, relative to addition to the model alkene 2. Addition to the 57 face of 1 occurs some 30% faster than addition to the... 

In the molecule (JT = F), the pupil-constricting action and toxicity are increased by a secondary grouping (e.g. R=R Me i = Me, i =Et RR = cydohexyl R = Me, ii = CHa CHMea). Furthermore, it appears that for non-cychc compounds both R and R, for the best results, must be unsubstituted hydrocarbon radicals (e.g. if = Me and R = COaEt the compound is scarcely toxic). Similarly, if ii=ii = CHaC3, both the myotic effect and toxicity are of a low order. Among unsubstituted (non-cychc) secondary radicals, the best results seem to be obtained when one group, at least, is Me for example, if i2 = i2 = Et, the toxicity is considerably reduced. 

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