Synthesis and reactivity of enantiomerically enriched thiiranium ions.

Enantiomerically enriched thiiranium ion 5 has been prepared by silver-assisted ionization of chloro sulfide 4 at -20 degrees C. This thiiranium ion is configurationally stable in solution up to room temperature as demonstrated by the stereospecific capture of the ion by various oxygen- and nitrogen-based nucleophiles. Both isolated olefins and weak Lewis bases can promote the racemization of 5 but these processes can also be suppressed at low temperature. Capture of 5 by methanol is faster than the racemization processes.