One-pot synthesis of 4-(phenylselanyl)-substituted pyrazoles

A facile, one-pot, general synthetic method for the preparation of 4-(phenylselanyl)pyrazoles is described. When reacted with hydrazines, alpha,beta-alkynic aldehydes produced in situ alpha,beta-alkynic hydrazones, which, upon treatment with phenylselenyl chloride, undergo cyclization to afford 4-(phenylselanyl)pyrazoles in good to high yields. This cyclization has been found to be general for a variety of in situ generated alpha,beta-alkynic hydrazones and exhibits good tolerance to a broad range of substituents, including electron-donating and electron-withdrawing groups. The enrichment of the pyrazole core with a selenyl moiety as well as with aryl and/or ferrocenyl groups may offer potential for the synthesis of molecules with pronounced or distinct biological activities