Potentially tautomeric 1,2,3,4-tetrahydro-1,4-dioxo-5H-pyridazino[4,5-b]indole

Article abstract of DOI:10.1016/S0040-4020(01)81802-0

The tautomeric 1,4-dioxygenated pyridazinoindole 1 exists in aqueous solution as a mixture of all four tautomeric forms 1a - 1d. The predominant tautomeric form is the 4-hydroxy-1-oxo compound 1b. The relative abundance of the four forms 1a ? 1b ? 1c ? 1d at equilibrium is 10^4.93:10^8.03:10^3.61:1