中文名称 | 英文名称 | CAS号 | 化学式 | 分子量 |
---|---|---|---|---|
—— | 3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one | 82507-66-2 | C9H9N3O | 175.19 |
Unambiguous syntheses of four unreported monomethylated derivatives of 3-phenyldihydro-1,2,4-triazin-6(1H)-ones, namely, the 1-methyl (2), 2-methyl (3), 4-methyl (4) and the imidic O-methyl derivative (5), are described. Regioselectivity was achieved for the synthesis of (2) by addition of ethyl glycinate to the 1,3-dipolar nitrile imine derived from N- methylbenzohydrazonoyl bromide hydrobromide (8). The key step for the synthesis of (3) was addition of benzyl 3-methylcarbazate (14) to ethyl N-[ chloro (phenyl) methylene ] glycinate (15b). The 4-methyl compound (4) was prepared by cycloaddition of ethyl N-( thiobenzoyl ) sarcosinate (21) with hydrazine hydrate, and the O-methyl compound (5) was prepared by reaction of sodium methoxide with 6-chloro-3-phenyl-4,5-dihydro-1,2,4-triazine (23).
Novel syntheses of 4,5-dihydro-1,2,4-triazin-6(1H)-ones were developed by use of imidoyl chlorides. The overall yield of 4,5-dihydro-1,2,4-triazin-6(1H)-ones prepared from amino acid imidates and hydrazines was improved by the 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 synthesized by cyclocondensation/cycloaddition pathways. Base-catalysed methylation of 3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one (15) gave the 1- methylated 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).
1-Methyl-3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one (1) undergoes aerial oxidation to give a mixture of 1- methyl-3-phenyl-1,2,4-triazin-6(1H)-one (2) and 1-methyl-3-phenyl-1,4-dihydro-1,2,4-triazine-5,6-dione (3). The dehydro derivative (2) was cleanly prepared by the oxidation of (1) with 2,3-dichloro-5,6-dicyano-1,4- benzoquinone (ddq). The dehydro derivative (2) underwent a surprising rearrangement to the triazole (12) upon oxidation with OxoneR. Several attempts at unambiguous synthesis of the α-dicarbonyl derivative (3) were unsuccessful; it was obtained, together with the 1,4-dimethyl derivative (13) by methylation of 3-phenyl-1,4- dihydro-1,2,4-triazine-5,6-dione (4) with sodium hydride and methyl iodide.