ASYMMETRIC ALDOL REACTIONS OF ACHIRAL 2-PHENYLSULFANYL ALDEHYDES WITHSMALL-SIZED AND MEDIUM-SIZED CARBOCYCLIC RINGS - THE SYNTHESIS OF HOMOCHIRAL SPIROCYCLIC LACTONES, PYRROLIDINES AND TETRAHYDROFURANS

Chiral boron enolates based on the 1,3-oxazolidin-2-one auxiliary reac t with achiral 1-phenylsulfanylcycloalkanecarbaldehydes in anti- and s yn-selective aldol processes to give the corresponding aldol products with moderate to excellent levels of diastereo- and enantio-control. S tereospecific cyclisation via an asymmetric episulfonium (thiiranium) ion leads to optically pure spirocyclic compounds in high chemical yie lds.