Asymmetric catalysis of the Diels-Alder reaction using dicationic zirconocene complexes

Enantio- and diastereoselective Diels-Alder reactions between dienophiles 1 and cyclopentadiene are catalyzed by a chiral, dicationic complex formed on. reaction of the chiral ansa-zirconocene 2 (X = Me) with 2 equiv of the strong acid [(Et2O)(2)H][B(Ar-F)(4)] (3; Ar-F = 3,5-(CF3)(2)C6H3), in either dichloromethane or 2-nitropropane solvent. The enantioselectivities are higher at lower catalyst loadings, particularly in dichloromethane solution, and spectroscopic studies suggest that this is related to competitive formation of ether-coordinated complexes at relatively low oxazolidinone:catalyst ratios.