ASYMMETRIC REACTIONS OF HIGH-SYMMETRY CHIRAL ORGANOSULFUR REAGENTS

It is standard practice in asymmetric synthesis to use optically active chiral auxiliaries derived from the ''natural pool''. Indeed, a large number of enantioselective syntheses are based on chiral auxiliaries such as camphor, menthol, tartaric acid, ephedrine, etc. which are obtained from nature. These auxiliaries can be modified to some extent in order to improve their ability to transmit the chiral information. Well-known examples are 8-phenyl menthol and several substituted camphor derivatives. However, by resorting exclusively to the chiral pool for auxiliaries, one is limited by the range of structural architectures available and sometimes limited by the possible future chemistry due to functional groups that the natural chiral auxiliary brings with it. The recent advances on the separation of enantiomers now make it possible to suggest synthetic chiral auxiliaries that can be planned in such a way to meet the desired requirements of simplicity, crystallinity, suitability for NMR and UV detection, etc. With these reagents, the extra steps required in resolution offset the drawbacks cited for the natural reagents. In other words, it might now be legitimate to design with indefinite freedom artificial chiral auxiliaries with a certain specific architecture for maximal chiral transmission. Imperative in this strategy is the achievement of high efficiency, high yield of products and general simplicity of operations. In this lecture, the results obtained with a reagent of this type and a few modification that can enlarge the potentiality of the synthetic concept, will be described. We have decided to investigate a