2,5-Dihydro-2,5-dioxo-3-methyl-3-pyrrole

Methyl 3-acyl-l-diphenylmethyleneamino-4,5-dioxo-4,5-dihydro-l//-pyrrole-2-carboxylates 489 are formed from 488 and oxalyl chloride in good yields. Preparative thermolysis of these compounds at 130-140°C gives mixtures of dipyrazolo[l,2- l,2- [l,2,4,5]tetrazines 491 as major products and pyrazoles 492 as minor hydrolytic by-products. The intermediacy of mesoionic compound 490 is expected (Scheme 83) <2004T5319>. 

H-(Furo[3,4-e indol> l,3-Dioxo-6-methyl-1,3-dihydro- E6b/1, 823 (aus Pyrrol-Der.)... 

Thermolysis of methyl l-methyleneamino-4,5-dioxo, 5-dihydro-lW-pyrrole-2-carboxylates 123 led to substituted dimethyl 3,9-dioxo-l,5,7,ll-tetrahydro-lA/,7A/-dipyrazolo l,2-a r,2 -<3 ][l,2,4,51tetrazine-l,7-dicarboxylates 124 <04T5319>. 

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>. 

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