Cysteine-derived thiazolidinethiones and serine-derived oxazolidinethiones serve as efficient chiral auxiliaries in boron-and tin-mediated aldol condensations. The condensations with a variety of simple aldehydes produced the expected erythro products in high chemical and optical yields. Additional advantages of these chiral auxiliaries were the ease of removal by methanolysis or hydroxaminolysis and their practical recyclability.
