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

Article abstract of DOI:10.1246/bcsj.73.681

Enantiopure 2-amino-3,3-diphenyl-1-propanol was synthesized by the hidantoin route starting from diphenyl-acetaldehyde followed by subsequent functional group transformations and optical resolution by a chiral HPLC. The amino alcohol can be converted into two new chiral ligands: 4,4'-bis(diphenylmethyl)-2,2'-bioxazoline and 2,2'-isopropylidenebis(4-diphenylmethyloxazoline), and further to complexes with copper(II) trifluoromethanesulfonate and nickel(II) perchlorate hexahydrate. The nickel(II) aqua complex obtained from the bisoxazoline effectively catalyzed the Diels-Alder reactions of cyclopentadiene with 3-acryloyl-2-oxazolidinone in high endo-selectivities and moderate enantioselectivities via a square planar transition structure.