Abstract Electron-rich 6-vinyl-and 6-(azavinyl) pyrimidinediones, such as 6- {[(dimethylamino) methylene] amino}-(1) and 6-[2-(dimethyl-amino) vinyl]-1, 3-dimethyl-2, 4 (1H, 3H)-pyrimidinediones (8), undergo cycloaddition reactions with electron deficient olefins to give pyrido [2, 3-d] pyrimidines (3a–e) and quinazolines (9a–c), respectively, after elimination of dimethylamine from the 1: 1 cycloadducts and oxidative aromatization. With ...