Abstract:The title compound was prepared in good yield by oxidation of 1-(hydroxymethyl)-5-methyl-3,6-dihydro-4H-pyridazino [4,5-b]carbazol-4-one with 2-iodoxybenzoic acid (IBX) in DMSO solution under very mild conditions. Keywords: pyridazino [4,5-b]carbazole; oxidation; 2-iodoxybenzoic acid; IBX In the course of our department's ongoing research in the field of antitumor agents [1-6], we previously reported the synthesis of a novel 3-aza analogue of the antitumor alkaloid, olivacine (1,5-dimethyl-6H-pyrido[4,3-b]carbazole) [7]. One of the compounds prepared in this context was the carbazole-fused hydroxymethylpyridazinone 1, which we had envisaged as a useful intermediate for the synthesis of new functionalized pyridazino [4,5-b]carbazoles with structural similarity to olivacine and related pyridocarbazoles. However, initial attempts to transform the hydroxymethyl group of 1 into an aldehyde or carboxylic acid functionality had given poor results, mainly because of the very low solubility of compound 1 in common solvents except dipolar aprotic solvents like DMSO. We now wish to report the convenient oxidation of 1 into the corresponding aldehyde 2 in DMSO solution, using a hypervalent iodine oxidizing agent.2-Iodoxybenzoic acid (IBX) was found to be the reagent of choice for this transformation, as it is typically used in DMSO solution at room temperature and permits the oxidation of alcohols into carbonyl compounds under very mild conditions [8]. As the only byproduct, one equivalent of 2-OPEN ACCESS

The title compound was prepared in excellent yield from 5-methyl-4-oxo-4,6-dihydro-3H-pyridazino[4,5-b]carbazole-1-carbaldehyde by treatment with hydroxylamine hydrochloride in formic acid without isolation of the intermediate oxime