AbstractNuclear magnetic resonance spectra have been utilized in several instances to distinguish between ring closure to a derivative of imidazo[1, 2‐c]pyrimidine or pyrrolo[2, 3‐d]pyrimidine. N.m.r. studies have also been employed to select Vc as the most probable structure for 5‐methylthio‐2, 7‐imidazo[1, 2‐c]pyrimidinedione. Ultraviolet absorption spectra and n.m.r. studies in deuterium oxide support the conclusion that there is more aromaticity in the anion V g than in the neutral molecule. The present work describes several new synthetic routes to derivatives of imidazo[1,2‐c]pyrimidine and pyrrolo[2,3