Synthesis of Selenium-Substituted Pyrroles and Pyrazol-3-ones

An approach to the synthesis of 4-(phenylseleno)pyrroles, 4-(phenylseleno)pyrazol-3-ones, and 4-(1,3-benzoselenazol-2-ylthio)pyrazol-3-ones is described. Their formation passes through hydrazonic intermediates obtained by the reaction between 1,2-diaza-1,3-butadienes and 1-(phenylseleno)ketones, phenylselenol, or 2-mercaptobenzoselenazole, respectively.