Síntese de 4-organosselanil-1H-pirazóis e calcogenocromen-4-onas utilizando metodologias verdes

Abstract

A simple and efficient method for the synthesis of 4-organoselanyl-1H pyrazoles has been developed, taking place under metal and halogen-free conditions. Electrophilic species of selenium were easily generated in situ by the reaction of diorganyl diselenides with Oxone® in ethanol as solvent in an open flask at 70 °C. These electrophilic selenium species were employed in the selenylation/cyclization of α,β-alkynyl hydrazones, giving the title compounds in moderate to excellent yields. The final species of selenium obtained from the reaction of diphenyl diselenide with Oxone®, were characterized by 77Se NMR spectroscopy and high-resolution mass spectrometry (HRMS). Further, an alternative green method was described for the synthesis of chalcogen-cromen-4-ones by the ring closure of 2-chloro ethynyl ketones with NaHY (Y = S, Se). These nucleophilic chalcogen species were generated in situ using NaBH4 to reduce elemental chalcogen using polyethylene glycol-400 (PEG 400) as the solvent. These reactions proceeded efficiently at 100 °C under argon, using a range of 2-chloro ethynyl ketones containing alkyl, aryl or vinyl groups and selenium or sulfur. By this efficient and simple approach, 9 selenochromen 4-ones and 9 thiochromen-4-ones were obtained in good to excellent yields after 2 h of reaction.