6-AZAPURINES .3. COVALENT SIGMA-ADDUCTS OF THE IMIDAZO[4,5-E]-AS-TRIAZINE RING-SYSTEM

7-Methylimidazo [4,5-e]-as-triazin-3(2H)-one, imidazo[4,5-e]-as-triazi n-3(2H)-one, and 5-methyl-imidazo [4,5-e]-as-triazin-3(2H)-one have be en synthesized from their respective 5,6-diamino-as-triazin-3-ones and selected one-carbon delivering reagents. These 6-azapurines undergo c ovalent hydration across the azomethine bond located in the imidazole portion of the ring. In water, the sigma-adducts ring open to certain as-triazin-3-ones whose structures were identified by NMR (H-1 and C-1 3) spectroscopy. These as-triazin-3-ones provided evidence for the des cribed mode of cleavage.