Preparation and structure determination of 1‐benzyl‐, 1‐methyl‐ and 1H‐5‐[(2‐nitro‐2‐phenyl)ethenyl]imidazoles

Abstract 1‐R‐5‐[(2‐Nitro‐2‐phenyl)ethenyl]imidazoles (R = Bn, Me, H) 6a,b,c were synthesized by the Knoevenagel reaction of the corresponding aldehydes 4a,b,c with phenylnitromethane 5. The E‐isomers 6a,b,c were precipitated from the reaction mixture as crystalline compounds in 89, 81 and 60% yields, respectively. Traces of the Z‐isomers 6a′b′,c′ were found in the reaction mixtures but could be obtained in a ratio of 4:3 from the E‐form with UV irradiation. The E‐forms were more stable and the Z‐isomers changed again to the E‐isomers in several weeks.