1,2,4-Triazines Dimroth rearrangement

Pyrimidin-5-amine, 4-methylamino-synthesis, 3, 121 Pyrimidin-5-amine, 4-oxo-purfne synthesis from, 5, 582 Pyrimidinamines acylation, 3, 85 alkylation, 3, 86 basic pXa, 3, 60-61 diazotization, 3, 85 Dimroth rearrangement, 3, 86 electrophilic reactions, 3, 68 Frankland-Kolbe synthesis, 3, 116 hydrolysis, 3, 84 IR spectra, 3, 64 N NMR, 3, 64 nitration, 3, 69 Principal Synthesis, 3, 129 reactivity, 3, 84-88 structure, 3, 67 synthesis, 3, 129 Pyrimidin-2-amines alkylation, 3, 61, 86 basic pK , 3, 60 diazotization, 3, 85 hydrogenation, 3, 75 hydrolysis, 3, 84 mass spectra, 3, 66 Pyrimidin-4-amines acidity, S, 310 alkylation, 3, 61, 86 basic pXa, 3, 61 Schifi base, 3, 85 synthesis, 3, 110, 114 1,3,5-triazines from, 3, 518 Pyrimidin-5-amines basic pXj, 3, 61 hydrogenation, 3, 75 reactions... 

Base-catalyzed Dimroth rearrangements of l-aryl-4,6-diamino-1,3,5-triazines or triflic acid-induced decomposition of 6-anilino-1,3,5-triazines led to the formation of the corresponding substituted 1,2-dihydro-l,3,5-triazines, whose structure was established on the basis of H NMR spectra (93JHC849). 

Diazotization of 5-amino[l, 2,3]triazole 692 afforded (88BSB179) triaz-olo[l, 5-i>][l, 2,4]triazine 694 as a result of a Dimroth rearrangement of the initially formed isomeric structure triazolo[5,l-c][l,2,4]triazine 693. Molecular structure of 694 was determined by single X-ray diffraction (Scheme 146). 

In addition to the Dimroth rearrangement of [l,2,4]triazolo[3,4-c][l,2,4]triazines discussed in the last section, derivatives of (42) would probably be accessible by the general application of a special case which involved the reaction of l-acetonyl-5-chloro-l,2,4-triazole (356) with hydrazine to produce the dihydro compound (357). Lead tetraacetate oxidation of (357) formed (358) (77JOC1018). 

Another example of a Dimroth rearrangement is the conversion of 2,4-bis(l-hydroxycyclo-alk-l-en-2-yl)-l,3,5-tria7ines 9 to (formylamino)pyrimidine derivatives 10. In this case, the triazine ring is not preserved as in the above examples. Again, the reaction is conducted in a refluxing aqueous ethanol solution.15... 

Some substituent replacements in this area follow pathways incorporating a Dimroth rearrangement. Thus, 3-alkylthio-4-aryl-l,2,4-triazin-5(4//)-one derivatives (197) react with ammonium acetate in acetic acid under reflux for 4 hours to give mainly the 3-arylamino-l,2,4-triazin-5(2//)-ones (198) 4-aryl-l,2,4-triazine-3,5(2/7,4//)-diones (199) are minor products (Equation (19)) <83H(20)5i>. 

Carbonyl diisocyanate (119) adds to iV-substituted amides to yield the unstable but isolable 1,3,5-oxadiazine-2,4(3//)-diones (120). However, with primary amides the resulting 1,3,5-oxa-diazinediones (120 = H) undergo a Dimroth rearrangement to the isomeric l,3,5-triazine-2,4,6-... 

Amination of 5-amino-6-aryl-l,2,4-triazine 4-oxides 133 with hydroxylamine hydrochloride or O-methylhydroxyl-amine in DMF results in 5-hydroxylamino-6-aryl-l,2,4-triazines 137 in 70-80% yields, thus indicating that the Dimroth rearrangement is involved (Scheme 72) <2000TL7379>. 

Several triazinyl ketones isomerize to 4-acetamidopyrimidines. TTiis is seen in the C-acylation of 2,4,6-trimethyl-l,3,5-triazine (708) with benzoyl chloride in the presence of sodium amide to give the ketone (709) which undergoes a Dimroth-like rearrangement in boiling water to afford A-(2-methyl-6-phenylpyrimidin-4-yl)acetamide (710) it can be seen that the acylating agent determines the identity of the 6-substituent 64JHC145). 

An unusual reaction involving s-triazine (247) and ethyl acetoacetate with sodium ethoxide leads eventually to the pyrido[4,3-ring opening and Dimroth-type rearrangement of the intermediate (248) (80JHC389>. 

Although these cyclizations were reported to give triazol[4,3-4/] [ 1,2,4]triazine, care should be taken because a Dimroth-like rearrangement could easily take place (Scheme 173). 

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