P-Bromobenzenesulfonate

Table S.16 presents data on some representative nucleophilic substitution processes. The first entry illustrates the use of 1-butyl-l-r/p-bromobenzenesulfonate to dononstrate at primary systems react with inversion, even under solvolysis conditkms in formic acid. The observation of inversion indicates a concerted mechanism in fids weakly nucleophilic solvent.

Like the un-ionized hydroxyl group, an alkoxy group is a weak nucleophile. Nevertheless, it can operate as a neighboring nucleophile. For example, solvolysis of the isomeric p-bromobenzenesulfonate esters 6 and 7 leads to identical prxKluct nuxtures, suggesting the involvement of a common intermediate. This can be explained by involvement of the cyclic oxonium icai which would result from intramolecular participation. ... 

The occurrence of nucleophilic participation is also indicated by a rate enhancement relative to the rate of solvolysis of n-butyl p-bromobenzenesulfonate. The solvolysis rates of a series of cu-mefhoxyall l p-bromobenzenesulfontes have been determined. A maximum rate is again observed where participation of a methoxy group via a live-membered ring is possible (see Table 5.20). 

The reactivity at the C-4 position of hexose and hexoside sulfonates has been demonstrated in the gluco and galacto series and could undoubtedly be extended to other sugars as well. In another example (25), methyl 2,3-di-0-benzoyl-4-0-p-tolysulfonyl-a-D-glucopyranoside (18a) was treated with potassium thiocyanate in N,N-dimethylformamide at 140°C. for 9 hours to give the C-4 epimeric thiocyanato derivative 19 in 34% yield. The corresponding 4-p-bromobenzenesulfonate (18b) however, afforded a 55% yield of 19 in only 2% hours of reaction time. 

It is evident from the foregoing sections that simple alkylvinyl halides do not react via an Sn 1 mechanism, if at all, even under extreme solvolytic conditions (146,149). More reactive leaving groups, such as arylsulfonates, were clearly needed to investigate the possible solvolytic behavior of simple alkylvinyl systems, but the preparation of vinyl sulfonates until recently was unknown. Peterson and Indelicato (154) were the first to report the preparation of vinyl arylsulfonates via reaction of the appropriate disulfonate with potassium t-butoxide in refluxing f-butanol. They prepared and investigated the solvolysis of 1-cyclohexenyl tosylate 169 and c/s-2-buten-2-yl tosylate 170 and the corresponding p-bromobenzenesulfonates (brosylates). Reaction... 

C40H47BrO 14S Tetra-O-acetyltrillenogenin mono-p-bromobenzenesulfonate TRLABS10 43 268... 

Figure 5.1 Effect of added LiC104 on ka and kt in solvolysis of threo-3-p-anisyl-2-butyl-p-bromobenzenesulfonate (3) in acetic acid. Reprinted with permission from S. Winstein and G. C. Robinson, J. Amer. Chem. Soc., 80, 169 (1958). Copyright by the American Chemical Society.

In 1897, it was observed889 that potassium iodide (in hot alcohol or acetone) converts ethyl p-bromobenzenesulfonate to ethyl iodide. Many years later, methyl and ethyl iodides 49 841 and ethyl a-iodopropionate808(b) were prepared in good yield by the action of the same iodide (in boiling water or alcohol) on the corresponding p-toluene-sulfonates. In these examples, the reaction obviously proceeded as an alkyl-oxygen fission, in accordance wi h the following equation ... 

A 68% yield of sodium p-bromobenzenesulfonate can be achieved by recrystallization of the sodium salt from water and a 70% yield of p-bromonitrobenzene by separation from the ortho isomer by recrystallization from EtOH. 

If the alcoholysis of the foregoing p-bromobenzenesulfonate esters is carried out with higher alcohols under reflux or with any alcohol in a pressure vessel at temperatures above 120°, partial isomerization at carbon atom 3 takes place, and mixtures of 3-normal- and 3-iso- 18-epi ethers are obtained. Of special interest is the alcoholysis effected with glycol monomethyl ether where separation of the mixture proved to be possible, as it is in many other cases. The 18-epi compound (XXXII) was antihypertensive, whereas the 3-iso-18-epi ether (XXXIII) had a stimulant activity. This was actually the first compound from any of the 3-iso series possessing any pharmacological activity. 

A non-halogen organic compound is used to form the threo and erythro isomers of Fe(CHDCHDCMe3)(CO)2(f -C5H,) fromMe3CCHDCHDOS02CsH4Br (vide infra). Alkyl p-bromobenzenesulfonate is used because the specific isomers can be efficiently made, are configurationally stable and are studied in other contexts. 

An isolated example of the use of x-ray diflraction analysis is provided by the work of Camerman and coworkers. Hydroformyl-ation of 3,4,6-tri-O-acetyl-D-glucal gave 4,5,7-tri-0-acetyl-2,6-anhydro-3-deoxy-D-gIuco- and -D-manno-heptitols, which were converted into the corresponding 1-p-bromobenzenesulfonates. One of these sulfonates was shown hy x-ray analysis to have the CJ(d) conformation in which all of the substituents are oriented equatorially hence, this sulfonate was the D-gluco isomer. 

Table 4.12. Relative Solvolysis Rates of Some w-Metboxyalkyl p-Bromobenzenesulfonates in Acetic Acid ...

In practical terms, it is usually possible to get high yields of para products from electrophilic substitution reactions of halobenzenes. Both nitration and sulfonation of bromobenzene give enough material to make the synthesis worthwhile. Although mixtures of products are always bad in a synthesis, electrophilic aromatic substitution is usually simple to carry out on a large enough scale to make separation of the major product, ideally by crystallization, a workable method. A 68% yield of sodium p-bromobenzenesulfonate can be achieved by recrystallization of the sodium salt from water and a 70% yield of p-bromonitrobenzene by separation from the ortho isomer by recrystallization from EtOH. 

Snyder originated the study of dideutereo-2-phenylethyl groups for determining the stereochemistry of displacement reactions. White-sides initiated the use of these systems in the study of organometallic systems through examination of the reaction of erythro-3,3-dimethylbutyl-l,2-rf2-p-bromobenzenesulfonate, 21, with [(C5H5)Fe(CO)2] (33) and the subsequent carbonyl insertion reaction promoted by triphenylphosphine (34). 

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