Menthyl arenesulfinates

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. 

The most important and widely used approach to chiral sulfoxides is the method developed by Andersen (5) based on the reaction between the diastereomerically pure (or strongly enriched in one dia-stereomer) menthyl arenesulfinates and Grignard reagents. The first stereospecific synthesis of optically active (+H7 )-ethyl p-tolyl sulfoxide 22 was accomplished in 1962 by Andersen (75) from (-)-(iS)-menthyl p-toluenesulfmate 45 and ethylmagnesium iodide. 

In menthyl arenesulfinates, the Cotton effect corresponding to the primary band has a high molecular amplitude and the negative sign characterizes the absolute configuration 5. 

Diastereomeric menthyl arenesulfinates as well as enantiomeric alkyl alkanesulfinates racemize in the presence of trichloroacetic anhydride even at room temperature (278). A mechanism based on kinetic investigations was proposed in which the formation of alkoxyacyloxysulfonium salt is the rate-determining step. 

The most important and w idely used approach to sulfoxides of high optical purity is based on the reaction of diastereomerically pure menthyl arenesulfinates with Grignard reagents. ( + )-(A)-l-Ethylsulfinyl-4-methylbenzene, prepared from (- j-menthyl (S)-4-mcthylbenzene-sulfmate and ethylmagnesium bromide, was the first optically active sulfoxide obtained by this method 13. 

The reaction was found to have proceeded [3,5] with complete inversion of configuration at sulfur. The absolute configuration of the menthyl arenesulfinate... 

Chiral pi-tolylsulfinyl naphthalene 48 is readily prepared by treating optically active (-)-menthyl (-)-arenesulfinates with arylmagnesium bromides Andersen, K. K., Gaffield, W., Papanikolaou, N. E., Foley, J. W., Perkins, R. I. (1964) J. Am. Chem. Soc., 86, 5637-5646. 

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

---