4-naphthyl-substituted Bis(oxazoline): A new, easily recoverable and efficient chiral ligand in asymmetric catalysis of the diels-alder reaction

Article abstract of DOI:10.1016/S0040-4020(98)00986-7

2,2-Bis{2-[(4R)-(2'-naphthyl)-1,3-oxazolinyl]}propane and its (45) enantiomer were prepared starting from 2-vinylnaphthalene, following the Sharpless protocol, and were found to be optically pure (ee ≥99.5%) by hplc analysis. These new bis(oxazolines) are efficient chiral ligands in the asymmetric catalysis of the Dieis-Alder reaction of Nalkenoyl-oxazolidin-2- one derivatives since endo cycloadducts are obtained with up to 94% ee. Different Lewis acids were tested, the best one being the Mg(II) cation derived from the corresponding triflate. A remarkable feature of such new chiral ligands is the low solubility in polar solvents, so that the chiral ligand can be easily recovered by a simple filtration. The recovered ligand can be directly reused in other asymmetric syntheses, without any further purification and, overall, without any drop in the induced enantioselectivities.