Bromobenzene, sulfonation

At an early date it was already recognized that the ketone (IX) derived from an oxidation of the C-18 carbinol function of methyl reserpate could be of considerable utility for further transformation of the reserpine pentacyclic ring system, but early attempts at the preparation of the desired compound by conventional oxidation, e.g., by Oppenauer s method, AAchlorosuceinimide, sodium dichromate, or chromic oxide in pyridine, were unsuccessful with both methyl reserpate and methyl 18-epireserpate. The ketone was finally obtained by heating methyl reserpate p-bromobenzene sulfonate with dimethyl sulfoxide in the presence of triethylamine (162), a method successfully used for simpler compounds (163). Subsequently, it was found that this oxidation could also be realized with other benzene sulfonate esters of methyl reserpate and 18-epireserpate. That the stereochemistry of the molecule was unaffected was proved by sodium borohydride reduction of the ketone, which gave equal amounts of methyl reserpate and its 18-epimer. This and other simple reactions of the ketone are sketched in Chart III, and additional observations will be given. 

An example of the Sn2 rate dependence on the nature of the counterion is given by the reaction of -butyl 4-bromobenzene sulfonate with lithium- and tetra-n-butylammonium halides in the weakly dissociating solvent acetone (cr = 20.6) [279]. 

Fumaric acid is photostable in the solid state. Its ammonium salt, however, photoreacted to give the syn [2-1-2] cyclobutane dimer (Scheme 50) [83]. N-(l-Octadecyl)-4-stilbazolium p-chloro- or p-bromobenzene sulfonate underwent quantitative photodimerization to give the syn head-to-head dimer (Scheme 51) [84]. The structure of the dimers from these photodimerization reactions indicates that a compulsory control of the stereochemistry by steric and coulombic repulsion was unsuccessful in these cases. We are now looking for other crystallographic strategies to synthesize the all-tranj-cyclobutane dimer of fumaric acid. 

Fig. 2. Hammett treatment of the acetolysis of t/2reo-3-aryl-2-butyl p-bromobenzene-sulfonates. Reproduced by permission of John Wiley and Sons.

Table 6. Rates and Products for the Formolyses of 3-(o-Methoxyphenyl)-l-propyl p-Bromobenzene-sulfonate (7i) and3-(o-Methoxyphenyl)-methyl-I-butyl Toluene-p-sulfonate (74) at 25°C ...

Table 8. Rates of Solvolysis of p-Bromobenzene-sulfonates in Acetic Acid" ...

A soln. of cyclohexyl benzenesulfonate in dimethyl sulfoxide heated 2 hrs. at 90-95 /130-160 mm in a Ng-atmosphere cyclohexene. Y 65%.—Dimethyl sulfoxide (also hexamethyl phosphoramide) functions as highly polar nonreacting solvent, and promotes the decomposition by an ionic path. The ease of decomposition increases in the order p-toluene-[Pg.481]

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