2.19 – 1,2,4-Triazines and their Benzo Derivatives

Aromatic Biheterocycles: Syntheses, Structures, and Properties

Publisher Summary Among the six-membered nitrogen-containing heterocycles the 1,2,4-triazines have attracted the attention of chemists for a long time. This is due to the fact that many 1,2,4-triazine derivatives are biologically active and are used in medicine and agriculture. Moreover, 1,2,4-triazines are of chemical interest. They proved to be very susceptible to attack by all kinds of nucleophiles, leading to the addition, and subsequently either substitution or cyclization, and ring transformation. This continuing and lively interest in this area of heterocyclic chemistry has produced a great number of publications and patent applications. This chapter concentrates on the behavior of monocyclic 1,2,4-triazines in reactions with C-, N-, 0-, and S-nucleophiles, because the important features of general character established for simple 1,2,4-triazines can evidently be applied to other derivatives including condensed 1,2,4-triazines.

Behavior of Monocyclic 1,2,4-Triazines in Reactions with C-, N-, O-, and S-Nucleophiles

Photochemistry of 0-quinones and α-diketones

Flash vacuum pyrolysis studies of substituted 6-acetoxy-2,4-cyclohexadienones (3 and 10) from 300 to 500 °C provide strong experimental evidence that direct [3,5]-sigmatropic rearrangements in these molecules are favored over the more familiar [3,3]-sigmatropic rearrangements. The preference holds when the results are extrapolated to 0.0% conversion, indicating that this is a concerted process. Pyrolysis of 6,6-diacetoxy-2-methyl-2,4-cyclohexadienone (9) at 350 °C gives a modest yield of the initial [3,5]-sigmatropic rearrangement product, 2,6-diacetoxy-6-methyl-2,4-cyclohexadienone (11). Qualitative arguments and electronic structure theory calculations are in agreement that the lowest energy pathway for each [3,5]-sigmatropic rearrangement is via an allowed, concerted pseudopericyclic transition state. The crystal structures of compounds 3, 9, and 10 prefigure these transition states. The selectivity for the [3,5] products increases with an increasing temperature. This unexpected selectivity is explaine...

Experimental and computational studies on the [3,3]- and [3,5]-sigmatropic rearrangements of acetoxycyclohexadienones: a non-ionic mechanism for acyl migration.

Grignard Reagents. XXIV. The Behavior of 3-Keto Derivatives of 1,2,4-Triazines toward Organomagnesium Halides, Lithium Aluminum Hydride, and p-Thiocresol

Photochemical Reactions in Sunlight. Experiments with 2-N-Phenyl-α,β-naphtho-1,2,3-triazolequinone and Monoxime Derivative in Sunlight and in Dark

6-Phenyl-3,5-dioxo-2,3,4,5-tetrahydro-1,2,4-triazine 1, 3-oxo-5,6-diphenyl-2,3-dihydro-1,2,4-triazine 3, 3,5,6-triphenyl-1,2,4-triazine 4, and 3-chloro-5,6-diphenyl-1,2,4-triazine 8, react with phenylmagnesium bromide. The reactions involved are represented by scheme A. Compound 3 reacts with o- and/or p-methoxyphenylmagnesium bromide to give compounds believed to have structures like 10 and 11 respectively. Compound 1 reacts with methylmagnesium bromide and with benzylmagnesium chloride to give products believed to have structures like 12a, b.

Hussein Abdel Azim Zaher

Papers

Grignard Reagents. XXIV. The Behavior of 3-Keto Derivatives of 1,2,4-Triazines toward Organomagnesium Halides, Lithium Aluminum Hydride, and p-Thiocresol

Photochemical Reactions in Sunlight. Experiments with 2-N-Phenyl-α,β-naphtho-1,2,3-triazolequinone and Monoxime Derivative in Sunlight and in Dark

The behaviour of some derivatives of 1,2,4-triazine toward organomagnesium halides

Das Verhalten einiger 1.2.4‐Triazin‐Derivate gegenüber Alkylmagnesiumhalogeniden, Diazomethan und in der Mannich‐Reaktion

Reactions of 2‐Aryl‐2H‐naphtho[1,2‐d]v‐triazole‐4,5‐quinones with aldehydes, alkenes and grignard reagents