This compound is obtained by reacting isocyanates of formula II [e.g. (S)-(+)-1-(1-naphthyl)ethyl isocyanate] with an α-ketocarboxylic acid derivative of formula III (R7 is H or lower alkyl) (e.g. ethyl 4-methylphenylpyruvate) in the presence of a base (e.g. triethylamine) ...