Treatment of trans-4-tert-butyl(diphenyl)siloxythiane oxide (6) with a homochiral lithium amide base, followed by electrophilic quench of the so-formed sulphoxide carbanion gives optically active products [e.g., (1R,2S,4R)-4-tert-butyl(diphenyl)-siloxy-2-trimethylsilylthiane 1-oxide (8)] in up to 69% ee.