Dihydro-1,2,4-triazin-6(1H)-ones. II - Synthesis of several methylated 3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-ones

Novel syntheses of 4,5-dihydro-1,2,4-triazin-6(1H)-ones were developed by u se of imidoyl chlorides. The overall yield of 4,5-dihydro-1,2,4-triazin-6(1 H)-ones prepared from amino acid imidates and hydrazines was improved by th e development of a much more efficient synthesis of the imidates. The new 1 ,2-, 1,4- and 5,5-dimethyl dihydro-1,2,4-triazin-6(1H)-ones have been synth esized by cyclocondensation/cycloaddition pathways. Base-catalysed methylat ion of 3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one (15) gave the 1-methyla ted derivative (8); under similar conditions 2-methyl-3-phenyl-2,5-dihydro- 1,2,4-triazin-6(1H)-one (9) afforded the 1,2-dimethyl derivative (7).