Asymmetric Synthesis of 3,3′-Pyrrolidonyl Spirooxindole-5′-Carboxylic Ester from l-Tryptophan

Abstract A highly efficient, multi-gram scale asymmetric synthesis of 3,3′-pyrrolidonyl spirooxindole-5′-carboxylic ester, which could be a potential precursor for the synthesis of cyanogramide, is accomplished from commercially available l-1-methyltryptophan in two pots. Fluoride-promoted desilylative spiro-cyclization of (semi) in situ generated isocyanate derived from l-1-methyltryptophan is the key reaction. Further, a variety of arene-substituted 3,3′-pyrrolidonyl spirooxindole-5′-carboxylxic acid esters were synthesized by late stage functionalization of easily accessible 3,3′-pyrrolidonyl spirooxindole-5′-carboxylic ester.