Stereoselective synthesis using a thiane oxide system as a disposable template
Substitution of the thiane oxide 1, via the corresponding α-sulfinyl carbanion, has been explored as a means of obtaining a range of functionalised products in stereoselective fashion. Whereas reaction of the α-sulfinyl carbanion derived from 1 with either Mel, BnBr or Me3SiCl results in substitution trans to the sulfoxide oxygen, e.g., to give 3–5, acylation occurs in a stereocomplementary fashion to give keto sulfoxide products with the new substitutent cis to the sulfoxide oxygen. The change in stereochemical outcome is accompanied by an inversion of the thiane oxide ring conformation, as demonstrated by X-ray crystallography. Subsequent manipulation of the initially obtained products was also examined, e.g. involving desulfinylation or thiane ring opening, to give useful products, such as epoxides, in stereoselective fashion.