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Synthesis of 3H-1,2,4-triazol-3-ones

Recent Literature

A nickel-promoted cascade annulation reaction of readily available hydrazonoyl chlorides and sodium cyanate provides 3H-1,2,4-triazol-3-ones in very good yields. The method has been successfully applied for the construction of the core skeleton of an angiotensin II antagonist.
S. Du, Z. Yang, J. Tang, Z. Chen, X.-F. Wu, Org. Lett., 2021, 23, 2359-2363.

An additive-free [3+2] cycloaddition reaction of hydrazonoyl chlorides with KOCN provides 1,5-disubstitued-3H-1,2,4-triazol-3-ones in EtOH at room temperature with KCl as the sole byproduct. Products can be easily precipitated after reaction completion using water.
I. Yavari, F. Gomoradi, O. Khaledian, Synlett, 2023, 34, 45-48.

A Pd-catalyzed three-component carbonylative reaction provides structurally diverses 3H-1,2,4-triazol-3-ones in good yields from hydrazonoyl chlorides and NaN3 through a cascade carbonylation, acyl azide formation, Curtius rearrangement, and intramolecular nucleophilic addition sequence. Benzene-1,3,5-triyl triformate (TFBen) has been used as a solid and convenient CO surrogate.
S. Du, W.-F. Wang, Y. Song, Z. Chen, X.-F. Wu, Org. Lett., 2021, 23, 974-978.

A selective, formal, 1,3-dipolar cycloaddition of organo-cyanamide ions with nitrile imine dipoles provides 1,2,4-triazol-3-imines. Hydrolysis of the 1,2,4-triazol-3-imines yields the corresponding 1,2,4-triazol-5-ones.
P. Sharma, S. V. Bhat, M. R. R. Prabhath, A. Molino, E. Nauha, D. J. D. Wilson, J. E. Moses, Org. Lett., 2018, 20, 4263-4266.