Chiral cyclopropyl-based PHOX ligands for intramolecular asymmetric Heck reaction

ORGN 640

Michael Rubin, and Marina Rubina, Department of Chemistry, Universtity of Kansas, 1251 Wescoe Hall Drive, RM 5088, Malott Hall, Lawrence, KS 66045
A novel class of chiral phosphanyl-oxazoline (PHOX) ligands with a conformationally rigid cyclopropyl backbone was synthesized and tested in the intermolecular asymmetric Heck reaction. Mechanistic modeling and crystallographic studies were used to predict the optimal ligand structure and helped to design a very efficient and highly selective catalytic system. Employment of the optimized ligands in the asymmetric arylation of cyclic olefins allowed for achieving high enantioselectivities and significantly suppressing product isomerization. Factors affecting the selectivity and the rate of the isomerization were identified. It was shown that the nature of this isomerization is different from that demonstrated previously using chiral diphosphine ligands.