Enantioselective hydrogenation of ethyl pyruvate over Pt/alumina: systematic variation of the modifier structure

A series of enantiomerically pure amino alcohols and amines has been prepared and tested as modifiers in the enantioselective hydrogenation of ethyl pyruvate over Pt/alumina. Systematic variation of the modifier structure revealed that an extended aromatic pi-system is necessary for the function of the modifier and that the enantioselectivity crucially depends on the structure of the amino function. Surprisingly simple modifiers such as 1-(l-naphthyl)ethylamine and 1-(9-anthracenyl)-2-(1-pyrrolidinyl)ethanol proved to be nearly as effective as 10,11-dihydrocinchonidine.