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Abstract
Systematic studies on the reactivity of the 1,2,3-triazine heterocycle are described.
A comprehensive study of the reaction scope of methyl 1,2,3-triazine-5-carboxylate (3a) with alkyl and aryl amidines is disclosed, reacting at room temperature at remarkable rates (< 5 min, 0.1 M in CH3CN) nearly 10000-fold faster than that of unsubstituted 1,2,3-triazine and providing the product pyrimidines in high yields. C4 Methyl substitution of the 1,2,3-triazine (3b) had little effect on the rate of the reaction, whereas C4/C6 dimethyl substitution (3c) slowed the room-temperature reaction (< 24 h, 0.25 M) but displayed an unaltered scope, providing the product pyrimidines in similarly high yields. Measured second-order rate constants of the reaction of 3a–c, the corresponding nitriles 3e and 3f, and 1,2,3-triazine itself (3d) with benzamidine and substituted derivatives quantitated the remarkable reactivity of 3a and 3e, verified the inverse electron demand nature of the reaction (Hammett ρ = −1.50 for substituted amidines, ρ = +7.9 for 5-substituted 1,2,3-triazine), and provided a quantitative measure of the impact of 4-methyl and 4,6-dimethyl substitution on the reactivity of the methyl 1,2,3-triazine-5-carboxylate and 5-cyano-1,2,3-triazine core heterocycles.
Simple and direct nucleophilic addition of secondary amines, including imidazole, to 1,2,3-triazine (3d) under mild reaction conditions (THF, 25–65 °C, 12–48 h), requiring no additives, cleanly provides β-aminoenals 9 in good yields (21 examples, 31–79%). The reaction proceeds by amine nucleophilic addition to C4 of the 1,2,3-triazine, in situ loss of N2, and subsequent imine hydrolysis to provide 9.
