Simple Approach to Highly Functionalized Trisubstituted Tetrahydropyrimidine-2,4-diones from Perhydropyrazino[1,2-f]pyrimidine-3,6,8-trione Precursors - Patiño-Molina, Rosario; García-López, M Teresa; Cenarruzabeitia, Edurne; Del Río, Joaquín; González-Muñiz, Rosario (Synthesis, 2007)