Base-mediated one-pot synthesis of 1,2,4-oxadiazoles from nitriles, aldehydes and hydroxylamine hydrochloride without addition of extra oxidant

A simple base-mediated one-pot synthesis of 3,5-disubstituted 1,2,4-oxadiazoles from nitriles, aldehydes and hydroxylamine hydrochloride has been developed, in which the aldehydes act as both substrates and oxidants. The reactions include three sequential procedures: base-promoted intermolecular addition of hydroxylamine to nitrile to lead to amidoxime, treatment of the amidoxime with an aldehyde to form 4,5-dihydro-1,2,4-oxadiazole, and oxidization of the 4,5-dihydro-1,2,4-oxadiazole by using another aldehyde to afford 1,2,4-oxadiazole. This method represents a direct and simple protocol for the synthesis of 3,5-disubstituted 1,2,4-oxadiazoles.