Arenesulfinates

Arenesulfinic acid, from ArNj 241 Aromaticity of boron hydrides 283 Arseno-de-diazoniation 275 Aryl anions 211... 

Preparation of enantiomerically pure sulfmate esters has most often been accomplished by making menthyl esters of arenesulfinic acids, particularly of p-toluenesulfinic acid. This... 

Aryl- and alkyl-magnesium halides were the first reagents used to form sulfoxides from sulfinate ester 19 and related (— )-menthyl arenesulfinates (equations 564,665,758 and 866). Whereas optically pure esters produced the homochiral sulfoxides shown in equations (5), (6) and (7), the ester shown in equation (8) was an oily mixture of four diastereomers which led to formation of a meso sulfoxide and a d, l pair enriched in one enantiomer. A homochiral sulfoxide was obtained by fractional crystallization. 

Additions of sulfinic acids to polyenes ( hydrosulfonylation ), however, proceed with very strong acids80 or under catalysis of Pd complexes81 (equation 17). With copper(II) arenesulfinates, azulene has been oxidatively sulfonylated in the 1- and 2-positions of the five-membered ring82 (equation 18). The sulfonylmercuration has also been applied with success to conjugated dienes83 (equation 19). 

In 1950, Cope and coworkers48 unsuccessfully attempted to use the well-known Meisenheimer rearrangement of N-allylamine oxides to 0-allylhydroxylamines49 in performing the formally analogous rearrangements of allyl aryl sulfoxides to allyl arenesulfenates and of allyl aryl sulfones to allyl arenesulfinates (equations 11-13). 

These authors48 have also examined the thermal stability of allylic arenesulfinates. They found that allyl, crotyl and a-methylallyl benzenesulfinates on heating underwent rearrangement to sulfones in low yields, but were unable to reach a decision with regard to reaction mechanism, mainly because the last two esters gave the same product crotyl phenyl sulfone. 

C. The [2,3]Sigmatropic Rearrangement of Propargylic Arenesulfinates to Allenyl Aryl Sulfones... 

Following studies on the rearrangement of allylic arenesulfinates, Braverman and coworkers have investigated a number of natural extensions of this unique transformation, including the predictable [2,3] sigma tropic rearrangements of allylic sulfenates to sulfoxides and of propargylic sulfenates and sulfinates to allenic sulfoxides and sulfones respectively. The last reaction is described below, while the other two are described in Chapter 14. 

In contrast to the allylic sulfenates mentioned so far, cinnamyl trichloromethanesulfenate (9), prepared by the usual method, can be isolated and is relatively stable. Furthermore, its rearrangement to cinnamyl trichloromethyl sulfoxide (i.e., without allylic isomerization, equation 7), proceeds at a relatively slow rate (in CC14 at 80.0 °C, k = 3.90 x 10 5s 1). This result also contrasts with the observation mentioned earlier that cinnamyl arenesulfinate rearranges to a-phenylallyl aryl sulfone33,34. Similar behavior has been detected for y, y-dimethylallyl ester 11 which undergoes thermal isomerization to sulfoxide 12 (equation 8)36-38. 

Arenesulfinate esters are usually prepared from an arenesulfinyl chloride and an alcohol in ether and pyridine. The arenesulfinyl chloride is usually prepared from the sodium arenesulfinate which is made by reduction of the arenesulfonyl chloride, preferably by aqueous sodium sulfite. After the crystalline sulfinate epimer has been removed by filtration, the equilibrium between the epimers remaining in the mother liquor may be reestablished by the addition of hydrogen chloride as shown by Herbrandson and Cusano . In this way the yield of the least soluble diastereomer may be increased beyond that which exists in the original reaction mixture (Scheme 1). Solladie prepared sulfinate ester 19 in 90% yield using this technique and published the details of his procedure. Estep and Tavares also published a convenient recipe for this method, although their yields were somewhat lower than Solladie s. 

As one can see, the rate of rearrangement of the allylic arenesulfinates in 60% ethanol-water shows a marked sensitivity to the substitution of an a- or y-hydrogen atom by an... 

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