The use of enantiomerically pure ketene dithioacetal bis(sulfoxides) in highly diastereoselective intramolecular nitrone cycloadditions. Application in the total synthesis of the β-amino acid (−)-cispentacin and the first asymmetric synthesis of cis-(3R,4R)-4-amino-pyrrolidine-3-carboxylic acid

Intramolecular 1,3-dipolar nitrone cycloaddition onto an enantiomerically pure ketene dithioacetal dioxide using a three-carbon tether gave the corresponding 5,5-disubstituted isoxazolidine as a single diastereomer in good yield. This reaction has been used as the key step in an asymmetric synthesis of the naturally occurring antibiotic, (−)-cispentacin. An asymmetric synthesis of 4-amino-pyrrolidine-3-carboxylic acid has also been carried out using the intramolecular nitrone cycloaddition as the stereocontrolling step.