Pyrrole studies: 31. The structures of potentially tautomeric 1,2-dihydro-6H-pyrrolo [3,4-d]pyridazine-1-ones and 1,2,3,4-tetrahydro-6H-pyrrolo [3,4-d]pyridazine-1,4-diones

Abstract

1,2-Dihydro-6H-pyrrolo[3,4-d]pyridazine-1-ones exist predominantly as such (104-47: 1) in equilibrium with the 1-hydroxypyridazine form, whereas 1,2,3,4-tetrahydro-6H-pyrrolo-[3,4-d]pyridazine-1,4-diones in equilibrium with the monohydroxy-oxo tautomeric forms are preferred by a factor of only ca. 100 : 1. It was not possible to determine the position of equilibrium between the 1-hydroxy-6H-pyrrolo[3,4-d]pyridazine-4-one and the 1,4-dihydroxy-6H-pyrrolo[3,4-d]pyridazine structures