Dihydro-1,2,4-triazin-6(1H)-ones. IV* Chemical Modification of 3-Phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-ones

Reaction of 3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one (1) and its 5,5-dimethyl derivative (4) with phosphorus pentasulfide gave the corresponding 6-thiones (2) and (5); methylation of (2) gave the 6-methylsulfanyl-3-phenyl-4,5-dihydro-1,2,4-triazine (3), also obtained by reaction of 6-chloro-3-phenyl-4,5-dihydro-1,2,4-triazine (8) with sodium thiomethoxide. Reaction of (8) with morpholine afforded the 6-(morpholin-4-yl) derivative (9). Reaction of (1) with isopropyl isocyanate gave N-isopropyl-6-oxo-3-phenyl-1,4,5,6-tetrahydro-1,2,4-triazine-1-carb-oxamide (19a), and a Mannich reaction of (1) with morpholine and formaldehyde gave the 1-morpholinomethylene derivative (20a). Attempts to effect cycloaddition of 1-methyl-3-phenyl-1,2,4-triazin-6(1H)-one (12) with a ben-zonitrile oxide failed. Reaction of the thione (2) with 1,3-dipolarophiles gave unstable adducts