摘要:
The regioselectivity of the palladium catalyzed allylic alkylation was studied systematically using bidentate ligands based on a xanthene backbone, bearing different donor atoms. The nature of the ligand donor atoms has a pronounced influence on the regioselectivity of the reaction. The results can be explained by a mechanism that distinguishes two 'stages' in the alkylation reaction. Ligands bearing strong pi-acceptor donor atoms induce the formation of branched products (60% for the P-P derivative), whereas the use of ligands with weak pi-acceptor donor atoms mainly yields linear products ( > 99% for the N-N derivative). (C) 2002 Elsevier Science B.V. All rights reserved.