ASYMMETRIC-SYNTHESIS OF CHIRAL SULFINYL DERIVATIVES USING (-)-MENTHYL 4-BROMOBENZENESULFINATE

The asymmetric synthesis of several new chiral 4-bromobenzenesulfinyl derivatives has been investigated, leading to alkyl 4-bromophenyl sulfoxides, 4-bromobenzenesulfinamides and alkyl 4-bromobenzenesulfinates in high enantiomeric excesses, All the new optically active sulfinyl derivatives have been obtained by nucleophilic displacement of the menthyloxy group on (-)-menthyl 4-bromobenzene-sulfinate having the (S) configuration at sulfur, as deduced from its X-ray crystal structure analysis, The sulfoxides and sulfinamides were prepared by using the appropriate Grignard reagent, whereas the alkyl sulfinates were prepared by using the acid-catalyzed alcoholysis of the above sulfinamides. It has been shown that the presence of the bromine atom in the para position on the benzene ring induced an important modification of the reactivity of these sulfinyl derivatives, in comparison with the classical corresponding paratoluenesulfinyl derivatives, In particular, the nucleophilic displacement was highly stereoselective at low temperature, which allowed the use of a large excess of nucleophilic reagent, leading in most cases to enantiomerically pure new chiral sulfinyl compounds in high yields. The optically active alkyl 4-bromobenzenesulfinates bearing a long n-alkyl chain are useful for the preparation of new chiral smectic C liquid crystals with ferroelectric properties.