Reductive coupling of new chiral auxiliaries derived from (S)-Indoline-2-carboxylic acid

Abstract

New chiral auxiliaries have been synthesized from (S)-indoline-2-carboxylic acid and various asymmetric reactions have been examined. Diastereoselective pinacol coupling reaction of a-ketoamides in the presence of samarium (II) iodide gave the outstanding results of (S,S)-threo-pinacols up to > 99% de. The pinacol coupled diol (S-indoline-(S,S)-threo-pinacol) was hydrolyzed to (2S,3S)-dialkylsubstituted tartaric acid as the almost optically pure form ( > 99% de). (S)-2-Alkoxymethylindoline was recovered in ca. 90% yield. It is the first time to obtain optically pure 2,3-disubstituted tartaric acids. The reductive coupling of a-aldiminoamides resulted in direct reduced amines without dimerization. The desired vicinal diamines could not be obtained.