Asymmetric Lewis acid mediated [1,2]-rearrangement of proline-derived ammonium ylides.

The first example of asymmetric Lewis acid mediated [1,2]-rearrangement of N-benzylic proline amides to form quaternary proline derivatives is reported. The presented reaction is shown to proceed with remarkable high C-->N-->C chirality transfer. Various quaternary proline derivatives have been prepared in good to excellent yields and high enantiomeric purity.