Efficient synthesis and structural analysis of new dioxopiperazine isoquinolines

We report herein the synthesis of new dioxopiperazine isoquinolines (5, 6), with a tetrahydro-6H-pyrazino[1,2-b]isoquinoline-1,4-dione moiety, using the Pictet-Spengler cyclization. The molecular structure of 6 was determined by RHF/3-21G and RB3LYP/6-31G(d) calculations. Both levels of calculations are in agreement with the X-ray data.