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

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.