A Versatile Synthesis of 6-Oxo-1,4,5,6-tetrahydro-pyrazine-2-carboxylic Acid Methyl Esters via MCR Chemistry - Illgen, Katrin; Nerdinger, Sven; Fuchs, Thilo; Friedrich, Corina; Weber, Lutz; Herdtweck, Eberhardt (Synlett, 2004)