Asymmetric Catalysis of the Diels−Alder Reaction Using Dicationic Zirconocene Complexes
Organometallics2000Vol. 19(6), pp. 947–949
Citations Over TimeTop 25% of 2000 papers
Abstract
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)2H][B(ArF)4] (3; ArF = 3,5-(CF3)2C6H3), 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.
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