F. Felluga et al., SYNTHESIS OF POLYSUBSTITUTED PYRROLIZIDINES FROM PROLINE DERIVATIVES AND CONJUGATED NITROOLEFINS, Helvetica Chimica Acta, 80(5), 1997, pp. 1457-1472
The stereochemistry of 1,3-dipolar cycloaddition of azomethine ylides
derived from aromatic aldehydes and L-proline alkyl eaters with severa
l nitroolefins was investigated. Cyclic and acyclic nitroolefins add t
o the anti form of the ylide in a highly diastereoselective but poorly
regioselective manner to give pyrrolizidine derivatives. In a few cas
es, the stereochemical results strongly support a stepwise mechanism.