RING ENLARGEMENT OF DIAZIRIDINONE WITH 2-SUBSTITUTED PYRROLE LEADING TO BICYCLIC TRIAZINE AND ITS TRANSFORMATION TO NOVEL MESOMERIC BETAINE

A ring enlargement reaction of a diaziridinone was investigated as a possible method for synthesizing heterobicyclic compounds having a bridgehead nitrogen atom. One of the products was transformed to a mesomeric betaine. Thus, the reaction of N,N'-di-tert-butyldiaziridinone (1) and deprotonated pyrrole-2-carboxaldehyde gave 2,3-di-tert-butyl-1-hydroxy-1,2,3,4-tetrahydropyrrolo[1,2-d][1,2,4]-triazin-4-one (4) in good yield. Similarly, 1 was treated with deprotonated imidazole-2-carboxaldehyde to afford the corresponding heterobicycle 5. Under similar conditions, pyrrole-2-carbonitrile gave an acyclic 1:1 adduct, 1-(N,N'-di-tert-butylcarbazoyl)-2-cyanopyrrole (8), which was successfully cyclized under acid catalysis to 2,3-di-tert-butyl-1-imino-1,2,3,4-tetrahydropyrrolo[1,2-d][1,2,4]triazin-4-one (9) and the de-tert-butylated product 10. A novel mesomeric betaine, 2-tert-butylpyrrolo-[1,2-d][1,2,4]triazinium-4-olate (11), was obtained along with its isomer 12 by acidic de-tert-butylation of 4.