Sulfinyldiacetic acid amide ester rac-1 was efficiently synthesized starting from thiodiacetic acid 4. Treatment was rac-1 with Ac2O and TMSOTf in CH2Cl2 at -40degreesC gave chemoselectively amide site alpha-acetoxy sulfide rac-2 in a ratio (91:9) of rac-2 and rac-3 and in a 90% total yield. Similar treatment of 1 with Ac2O and TMSOTf in DMF at room temperature furnished ester site alpha-acetoxy sulfide rac-3 in a highly chemoselective manner (rac-2:rac-3 = 3:97) and in a 92% total yield. (C) 2002 Elsevier Science Ltd. All rights reserved.