Rearrangement of 3,3-disubstituted 1-aryl-4,5-dihydro-5-oxo-3H-1,2,4-triazolium tetrafluoroborates; Part 3. An efficient synthesis of 1,5-heteroannulated 1,2-dihydro-2-phenyl-3H-1,2,4-triazol-3-ones

Article abstract of DOI:10.1055/s-1990-27090

1-Isocyanato-1-(phenylazo)heterocycloalkanes 3a-f react with tetrafluoroboric acid to yield the respective 3-spiro-substituted 4,5-dihydro-5-oxo-1-phenyl-3H-1,2,4-triazolium tetrafluoroborates 4a-f. These compounds rearrange under ring enlargement in good yields to 1,5-heteroannulated 1,2-dihydro-2-phenyl-3H-1,2,4-triazol-3-ones 5a-f. In two special cases, 4,5-heteroannulated 2,4-dihydro-2-phenyl-3H-1,2,4-triazol-3-ones 7g,h are obtained.