HNO2-Assisted Triazine Cycle Contraction in 3-oxo-,3-thioxo- and 3-imino-5,7-dimethyl-4a,7a-diphenyl-perhydroimidazo[4,5-e][1,2,4]triazin-6-ones

Treatment of 3-oxo-, 3-thioxo- and 3-imino-5,7-dimethyl-4a,7a-diphenylperhydroimidazo[4,5-e][1,2,4]triazin-6-ones with NaNO₂ in the presence of AcOH caused contraction of the perhydrotriazine cycle to the imidazolidine one. The products were transformed into glycolurils and their analogues.