Synthesis of C2-symmetric tris-thioethers via optically active mustards

Chiral dihydroxy thioethers derived from l-mandelic and l-lactic acid are activated with SOCl2, SOBr2 and by bis-trifluoroacetate formation to give optically active mustard gas analogues. These compounds serve as substrates for stereospecific nucleophilic substitution reactions with NaSEt and NaSPh to furnish C2-symmetric tris-thioethers with overall inversion of configuration.