title: Phosphite-oxazole/imidazole ligands in asymmetric intermolecular Heck reaction.
abstract: We describe the application of a new class of ligands--the phosphite-oxazole/imidazole (L1-L5a-g)--in asymmetric intermolecular Pd-catalyzed Heck reactions under thermal and microwave conditions. These ligands combine the advantages of the oxazole/imidazole moiety with those of the phosphite moiety: they are more stable than their oxazoline counterparts, less sensitive to air and other oxidizing agents than phosphines and phosphinites, and easy to synthesize from readily available alcohols. The results indicate that activities, regio- and enantioselectivities, are highly influenced by the type of nitrogen donor group (oxazole or imidazole), the oxazole and biaryl-phosphite substituents and the axial chirality of the biaryl moiety of the ligand. By carefully selecting the ligand components, we achieved high activities, regio- (up to 99%) and enantioselectivities (up to 99%) using several triflate sources. Under microwave-irradiation conditions, reaction times were considerably shorter (from 24 h to 30 min) and regio- and enantioselectivities were still excellent.
authors.affiliation: Departament de Química Física i Inorgànica. Universitat Rovira i Virgili, Campus Sescelades, C/Marcel·lí Domingo, s/n. 43007 Tarragona, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Mazuela
authors.forename: Paivi
authors.initials: P
authors.lastname: Tolstoy
authors.forename: Oscar
authors.initials: O
authors.lastname: Pàmies
authors.forename: Pher G
authors.initials: PG
authors.lastname: Andersson
authors.forename: Montserrat
authors.initials: M
authors.lastname: Diéguez
mesh_terms: D005663:Furans / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry*; D008024:Ligands; D008872:Microwaves; D015394:Molecular Structure; D010080:Oxazoles / Q000737:chemistry*; D017905:Phosphites / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D005663:Furans; D007093:Imidazoles; D008024:Ligands; D010080:Oxazoles; D017905:Phosphites; C073812:2,3-dihydrofuran; C029899:imidazole