Reusable nano-sized chiral bisoxazoline catalysts

The nano-sized gold particle-based chiral catalyst having two kinds of alkyl thiol spacers, one of which is substituted with the chiral bisoxazoline/copper(II) complex at the end, behaves as reusable homogeneous catalyst. This gold particle complex acts as nearly homogeneous catalyst in the ene reaction between 2-phenylpropene and ethyl glyoxylate in dichloromethane, while it undergoes dense aggregation when diluted with hexane so as to be separated by simple filtration. Thus, the catalyst can be recovered after the completion of reaction by the repeated sequences of solvent exchange, centrifugal treatment, and decantation, followed by the recharge of substrates, and the situation is ready for the second reaction. (c) 2005 Elsevier Ltd. All rights reserved.