From 1,3,5-Triazines

Many of the reactions discussed in this section can be treated as syntheses of 1,2,4-triazines from more than one fragment. 

Only a few reactions are known which can be treated as synthetic methods for 1,2,4-triazines from two three-atom fragments. 

In the previous chapters we mentioned a number of reactions which can be treated as methods for the preparation of 1,2,4-triazines from more than two fragments since one of the starting materials is prepared from two or three compounds. Here we present some further reactions. 

Scheme 14.1 Formation of 3-amino-1,2,4-triazines from aminoguanidine and deoxyglu-...

The mass spectrum of the unsubstituted 1,2,4-triazine shows peaks at mjz = 81, 53, 52, 51, 40, 39, 38, 28, 27, 26, and 25, being accounted for in part by the fragmentation pattern given below. The fragmentation pattern was confirmed by the mass spectrum of [2H3]-l,2,4-tri-azine.105 [4-15N]-3-Methyl-l,2,4-triazine shows a similar fragmentation pattern,106 as do most alkyl- and aryl-substituted 1,2,4-triazines. From these data it follows that the fragmentation starts with loss of nitrogen. 

The reaction of a fMactone with 4-isonitroso-3-methyl-l-phenylpyrazol-5-one to give a 1,2,4-triazine-5,6(177,4/7)-dione is the only reported synthesis of a 1,2,4-triazine from a four-mem-bered heterocycle.230... 

For the formation of 5-[(hydroxyimino)alkyl]-1,2,4-triazines from 1,2,4-triazines and nitronates, see Houben-Weyl, Vol. E14b, p 854. 

In the previous sections a number of reactions were mentioned which could be treated as methods for the preparation of 1,2,4-triazines from more than two fragments since one of the starting materials is prepared from two or three compounds. A further example (a [3 + 2 + 1] combination otherwise a [5 + 1]) is seen when salicylhydrazide (454), ammonium acetate, and a 1,2-dicarbonyl compound are heated at reflux in acetic acid 3-(2 -hydroxyphenyl)-l,2,4-triazines (455) are formed (Equation (61) cf. (425) (426) in Scheme 79) <89JOCl245>. 

Guanidines, sec. amines,- and benz 0-1,2,4-triazines from sulfonylguanidiites... 

The triazine ring system is a component of commercial dyes, herbicides, insecticides, and even pharmaceutical compounds. By application of microwave technology, a general procedure has been developed for rapid synthesis of diverse 3,5,6-trisubstituted 1,2,4-triazines from a variety of 1,2-diketones and acyl hydrazides in excellent yields and purities (Scheme 10.52) [107]. 

Various modifications of this approach are demonstrated by the synthesis of condensed 1,2,4-triazines from 1,2-dioxo compounds and ortAo-amino derivatives of A -aminoazoles or A -aminoazines (Schemes 139-141) <1997J(P1)1829, 2000M487, 2001CPH77, 2002JC0419>. 

Another pattern for the synthesis of 1,2,4-triazines from [6+0] fragments is the intramolecular Cs-Nj bond formation which takes place in the intramolecular cyclization of hydrazones 290 derived from the reaction of... 

Conversion of azlactones to other heterocyclics 1,2,4-Triazines from 4-alkylidene-5-oxazolones... 

Triazines from 4-alkylidene-5-oxazolones via a-ketocarboxylic acid thiosemicarbazones s. 18, 475 ring closure s. a. Pharmazie 20, 75 (1965)... 

Triazines from a-ketocarboxylic acids via a-ketocarboxylic acid tbiosemicarbazones... 

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