Rearrangement of 3,3-Disubstituted 1-Aryl-4,5-dihydro-5-oxo-3H-1,2,4-triazolium Tetrafluoroborates; Part 2. A Convenient Synthesis of 1,5-Annulated 1,2-Dihydro-2-phenyl-3H-1,2,4-triazol-3-ones

Article abstract of DOI:10.1055/s-1990-27022

1-Isocyanato-1-(phenylazo)cycloalkanes 3 react with tetrafluoroboric acid to yield 3-spiro substituted 4,5-dihydro-5-oxo-1-phenyl-3H-1,2,4-triazolium tetrafluoroborates 4.Compounds 4 rearrange with ring expansion in good yield to give, after basic workup,