1.2.4- Triazines reactions with DMAD

Interesting results were obtained by reaction of substituted 1,2-dihydro-1,3,5-triazines with esters of acetylenedicarboxylic acid (DMAD) and of propiolic acid.254 In the case of the reaction with DMAD, formation of the different products 175 and 176 has been reported,254 presumably due to differences in the nucleophilicity of the secondary nitrogen atom of the triazines. 

Rees et a/.480 461 heated 2-methylnaphtho[l,8-cfe]triazine (505) with DM AD and EP in o-dichlorobenzene and obtained 30-40% of 2-methylacenaphtho[5,6-dehydrogenating agent this must facilitate the transformation of 506 to 507. The product is a stable 14rr aromatic system, possibly formed by a 1,11-dipolar (127r + 2n) cycloaddition. A similar reaction with the naphtho[l,8- /]thiadia-zine (508) and DMAD giving 509 was described.480... 

Unstable furo[2,3-d]-1,2,3-triazoles are intermediates in the cycloaddition reaction of 1,2,3-tri-azolium 1-oxides to yield 1,2,3-triazines. For example, compound (28) reacted with DMAD to give initially the 1,3-dipolar cycloadduct (29). Rearrangement of this adduct (29) gives the unstable furo[2,3-d]-1,2,3-triazole derivative (30) which rearranges further to yield 1,2,3-triazine (32) via the intermediate (31) (Scheme 2) <90JCS(Pl)332l>. 

An unusual example of synthesis of pyrimido[l,2-fe][l,2,4]triazine (71) involved the reaction of 1-amino-2-hydrazinopyrimidine-6-ones (69) with DMAD. TTie hydrazone intermediates (70) when heated under reflux in acetic acid underwent an interesting ring opening/reclosure resulting in the synthesis of pyrimido[l,2-Z>][l,2,4]triazine (71) (Scheme 4) <88JHC739>. 

Addition of DMAD to some S-oxoalkyl-s-triazines (278) leads to 280,357 and the ease of reaction is dependent on the substituents on the triazine ring. The stereochemistry of the adduct (279) from EP is in agreement with the cyclic mechanism leading to a cis addition of the dienophile to the enol,358 and bicyclic products were not obtained. 

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