Schiff bases condense with 2-oxazolin-5-ones having a C-4 methylene and/or C-2 methyl group, and the reaction in glacial acetic acid, containing freshly fused sodium acetate, produces 4-arylidene- and/or 2-styryl-2-imidazoline-5-ones as a result of simultaneous introduction of arylidene and amino moieties.