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-di methyl 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-ph enyl-4,5-dihydro-1,2,4-triazine (8) with sodium thiomethoxide. Reaction of (8) with morpholine afforded the 6-(morpholin-4'-yl) derivative (9). Reacti on of (1) with isopropyl isocyanate gave N-isopropyl-6-oxo-3-phenyl-1,4,5,6 -tetrahydro-1,2,4-triazine-1-carboxamide (19a), and a Mannich reaction of ( 1) with morpholine and formaldehyde gave the 1-morpholinomethylene derivati ve (20a). Attempts to effect cycloaddition of 1-methyl-3-phenyl-1,2,4-triaz in-6(1H)-one (12) with a benzonitrile oxide failed. Reaction of the thione (2) with 1,3-dipolarophiles gave unstable adducts.