1 INTRODUCTION

Enantioselective hydrogenation of carbon-carbon double bonds using cinchona-modified Pd has received much attention. ^{1 5} The highest enantioselectivities have been achieved using reactants which possess an acidic moiety, such as ?, ?-unsaturated carboxylic acids (50 72%) ^{1 5} and hydroxypyrone (~86%).6 The enantioselectivities achieved have been attributed to the crucial role that the acidic function plays in interaction with the quinuclidine-N atom of the adsorbed modifier. This interaction is not available to the corresponding ?, ?-unsaturated esters and hence, under the same experimental conditions, no enantioselectivity is observed.2 Here we report the first enantioselective hydrogenation of an unsaturated ester over a cinchona-modified heterogeneous metal catalyst; this has been achieved by further functionalisation of the ester so as to restore the possibility of a reactant-modifier interaction. The target reaction in this work has been the hydrogenation of N-acetyl dehydrophenylalanine methyl ester (I) to N-acetyl phenylalanine methyl ester (Figure 1). The target reaction is catalysed by Rh(DIPAMP)-complexes in solution7 and by these complexes supported on oxides.

Figure 1: Hydrogenation of N-acetyl dehydrophenylalanine methyl ester (I)