Synthesis of 1,2‐diaryl‐2‐imidazolines

Polyphosphoric acid and N‐aryl‐N′‐benzoylethylenediamines in a type of Bischler‐Napieralski reaction afforded 1,2‐diaryl‐2‐imidazolines in good yields, rather than the 2,3‐dihydro‐1H‐[1,4]‐benzodiazepines. Blocking of the amino nitrogen by a methyl or ethyl group, to avoid imidazoline formation, gave starting material rather than the expected dihydrobenzodiazepine. When p‐tosyl was the blocking group, imidazoline was again the only product isolated. Analytical and spectroscopic data of several unreported 1,2‐diaryl‐2‐imidazolines are presented.