Stereodivergent methodology for the synthesis of complex pyrrolidines

The intramolecular reaction of oxime ethers and cyclopropane diesters results in the diastereoselective formation of substituted pyrrolo-isoxazolidines which serve as precursors to the ubiquitous pyrrolidine motif. A simple reversal of addition order of catalyst and substrate results in formation of two discrete diastereomers in a highly selective and predictable manner. The adducts are prepared in excellent yields from either enantiomer of an alkoxyamino-tethered cyclopropanediester, allowing efficient access to highly substituted homochiral pyrrolidines.