Effect of catalysts on the Fischer cyclization of cyclohexanone 4-pyridylhydrazone
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The peculiarities of the Fischer cyclization of cyclohexanone 4-pyridylhydrazone and the formation of 5,6,7,8-tetrahydro-γ-carboline, 4-aminopyridine, 4-ethylaminopyridine, 4-pyridone, and 2-(4-pyridyl)-3,3a,4,5,6,7-hexahydroindazole-3-spirocyclohexane under the conditions of this reaction are examined. In the case of I, as also for the isomeric 2-pyridylhydrazones, catalysts can be arranged in the following order with respect to their ability to increase the yield of the normal indolyzation product: cuprous chloride ≈ sulfosalicyclic acid < polyphosphoric acid < p-toluenesulfonic acid < zinc chloride. It was established that the indolyzation of I proceeds also without acid catalysts under the influence of sodium ethoxide.
KeywordsSodium Chloride Zinc Organic Chemistry Acid Catalyst
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