Pyranoside Phosphite–Oxazoline Ligands for the Highly Versatile and Enantioselective Ir-Catalyzed Hydrogenation of Minimally Functionalized Olefins. A Combined Theoretical and Experimental Study
作者:Javier Mazuela、Per-Ola Norrby、Pher G. Andersson、Oscar Pàmies、Montserrat Diéguez
DOI:10.1021/ja204948k
日期:2011.8.31
A modular set of phosphite-oxazoline (P,N) ligands has been applied to the title reaction. Excellent ligands have been identified for a range of substrates, including previously challenging terminally disubstituted olefins, where we now have reached enantioselectivities of 99% for a range of substrates. The selectivity is best for minimallyfunctionalized substrates with at least a moderate size difference
Novel 8-alkyl- or 2-aryl-4,5-(4,6-O-benzylidene-3-O-(diphenylphosphino)-1,2-dideoxy-alpha-D-glucopyrano)-[2,1-d]-2-oxazolines (5a-f) have been prepared from D-glucosamine hydrochloride. They work effectively as chiral ligands and provide a high level of enantiomeric excess in palladium-catalyzed allylic alkylation and amination reactions. The allylic alkylation of 1,3-diphenyl-3-acetoxyprop-1-ene with dimethyl malonate proceeds smoothly in the presence of 0.25 mol % [Pd(eta(3)-C3H5)Cl](2) and the chiral ligand 5a having the smallest substituent on oxazoline at 0 degrees C within 6 h to furnish the highest enantiomeric excess (96% ee). The Ligand 5a is also effective for the Pd-catalyzed amination of ethyl 1,3-diphenylprop-2-enyl carbonate, leading to the corresponding allylic amine in 94% ee. The full scope and limitations using ligands 5a-f in the allylic substitution reactions are described.