Dimethyl dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate

Tautomerism of tetrazines was investigated by ID 15N INADEQUATE.85 Dimethyl dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate can exist either in 1,2- (8) or... 

Cycloaddition of dimethyl l,2,4,5-tetrazine-3,6-dicarboxylate with EWG-substituted primary ketene N,0-acetals provides a tetrasubstituted pyridazine, methyl 4-amino-5,7-dioxo-6,7-dihydro-5/7-pyrrolo[3,4-4pyridazine-3-carboxylate <200681513>. 

The submitters employed, without purification, thionyl chloride obtained from Fisher Scientific Company. The procedure should be performed in a well-ventilated hood since thionyl chloride Is a lachrymator. The yield of dimethyl ester was found to be lower in instances when the thienyl chloride-methanol solution was not allowed to stir (30 min, -30°C) prior to the addition of dihydro-1,2,4,5-tetrazine-3,6-dicarboxylic acid. 

Liberating the acid from the disodium salt with H2S04 decreases the yield of this step considerably. Dimethyl t,4-Dihydro-i,2,4J-tetrazine-3,6-dicarboxylate (2b) ... 

Similarly, heating of methyl 3-acyl-l-(diphenylmethyleneamino)-4,5-dioxo-4,5-dihydro-l//-pyrrole-2-carboxylates 96 gave the corresponding dimethyl 2,8-diacyl-3,9-dioxo-5,5,ll,ll-tetraphenyl-3,5,9,lTtetrahydrodipyrazolo[l,2- 7 l, 2 -i [l,2,4,5]tetrazine-l,7-dicarboxylates 99 in good yields. The proposed mechanism involves thermal decarbon-ylation to give the ketene intermediate 97, which cyclizes into the azomethine imine 98, followed by dimerization (Scheme 24) <2004T5319>. 

An intriguing reaction of dimethyl l,2,4,5-tetrazine-3,6-dicarboxylate 150 with tricyclic sulfone 188, leading to the fused 5,6-dihydro-l,2-diazocine 190, was reported recently by Paquette etal. Presumably, compound 190 was formed by retrograde elimination of the nitrogen in the initially formed [4+2] cycloadduct 189 via cleavage of the cyclobutane ring (Scheme 50) <20040L1313>. 

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