title: On the role of chiral catalysts in the alkenyl zirconocene/zinc addition to aldehydes: a study of ligand loading and asymmetric amplification.
abstract: Unusual nonlinear asymmetric amplification and chiral ligand loading effects were discovered for the use of catalytic quantities of chiral aminoalcohols in the in situ hydrozirconation-transmetalation-aldehyde addition processes. While the stereochemically most efficient aminothiol ligands demonstrated mechanistically conventional reaction parameters in excellent agreement with Kagan's ML(2) system, the asymmetric induction in the presence of a chiral aminoalcohol was found to vary greatly with loading and %ee of the ligand. Aminothiols remain the ligands of choice for the highly enantioselective formation of allylic alcohols and provide experimentally more predictable reaction variables. However, new, optimized conditions lead to a synthetically useful product %ee using the readily available and scalable aminoalcohol 2a.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA. pwipf@pitt.edu
authors.forename: Peter
authors.initials: P
authors.lastname: Wipf
authors.forename: Nilukshi
authors.initials: N
authors.lastname: Jayasuriya
authors.forename: Seth
authors.initials: S
authors.lastname: Ribe