Bisoxazoline and bioxazoline chiral ligands bearing 4-diphenylmethyl shielding substituents. Diels-Alder reaction of cyclopentadiene with 3-acryloyl-2-oxazolidinone catalyzed by the aqua nickel(II) complex

Enantiopure 2-amino-3,3-diphenpt-1-propanol has been synthesized by the hid antoin route starting from diphenylacetaldehyde, followed by subsequent fun ctional group transformations and optical resolution by a chiral HPLC. This amino alcohol can be converted into two new chiral ligands: 4,4'-bis(diphe nylmethyl)-2,2'-bioxazoline and 2,2'-isopropylidenebis (4-diphenylmethyloxa zoline), and further to complexes with copper(II) trifluoromethanesulfonate and nickel(II) perchlorate hexahydrate. The nickel(II) aqua complex derive d from the bisoxazoline effectively catalyzes the Diels-Alder reactions of cyclopentadiene with 3-acryloyl-2-oxazolidinone in high endo-selectivities and moderate enantioselectivities through a square planar transition struct ure.