Investigation of the importance of nitrogen substituents in a N-P chiral ligand for enantioselective allylic alkylation

The synthesis of three chiral chelate nitrogen-phosphorus (S)-valine derived ligands with the potential fur stereogenic nitrogen donation is described. In palladium catalysed allylic substitution reactions the ligands induced varying enantioselectivities ranging From 92%, e.e. of the (R)-enantiomer to 83% e.e. of the (S)-enantiomer. Structural and spectroscopic investigations into the origin of this effect were conducted, but were inconclusive. However, the importance of the consideration of N-substituents in such systems is highlighted. (C) 2001 Elsevier Science Ltd. All rights reserved.