Premium
Modular Phosphite–Oxazoline/Oxazine Ligand Library for Asymmetric Pd‐Catalyzed Allylic Substitution Reactions: Scope and Limitations—Origin of Enantioselectivity
Author(s) -
Diéguez Montserrat,
Pàmies Oscar
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701636
Subject(s) - moiety , oxazoline , allylic rearrangement , chemistry , ligand (biochemistry) , substitution reaction , stereochemistry , catalysis , nucleophile , alkyl , combinatorial chemistry , medicinal chemistry , organic chemistry , receptor , biochemistry
Abstract A library of phosphite–oxazoline/oxazine ligands L1 – L15 a – h has been synthesized and screened in the Pd‐catalyzed allylic substitution reactions of several substrate types. These series of ligands can be prepared efficiently from easily accessible hydroxyl amino acid derivatives. Their modular nature enables the substituents/configurations in the oxazoline/oxazine moiety, alkyl backbone chain and in the biaryl phosphite moiety to be easily and systematically varied. By carefully selecting the ligand components, therefore, high regio‐ and enantioselectivities ( ee values up to 99 %) and good activities have been achieved in a broad range of mono‐ and disubstituted linear hindered and unhindered liner and cyclic substrates. The NMR studies on the Pd–π‐allyl intermediates provide a deeper understanding about the effect of the ligand parameters on the origin of enantioselectivity. It also indicates that the nucleophilic attack takes place predominantly at the allylic terminal carbon atom located trans to the phosphite moiety.