Imidazo[2,1-b]thiazoles, imidazo[2,1-b]imidazoles and Pyrrolo[1,2-c]imidazoles. synthesis, structure and evaluation of benzodiazepine receptor binding

As a continuation of our studies on bicyclic heterocycles with benzodiazepine receptor affinity, derivatives with a 5:5 bicyclic skeleton, namely imidazo[2,1-b]thiazoles, imidazo[2,1-b]imidazoles and pyrrolo[1,2-c]imidazoles were prepared. The compounds possessed an aromatic substituent with different spatial arrangement and distance to the bicyclic skeleton. X-ray structure analysis was performed for Z-2-(4-chlorobenzylidene)-5,5-diphenyl-2,3,5,6-tetrahydroimidazo[2,1-b]imidazoline-3,6-dione (6a) and 5-amino-6-cyano-7-phenyl-1-oxo-3-thioxo-2,3-dihydro-1H-pyrrolo[1,2-c]imidazole (20a). In contrast to the previously described arylideneimidazo[2,1-b]thiazepinones the smaller heterocyclic ring systems investigated in this study were devoid of meaningful benzodiazepine receptor affinity as well as anti-convulsant activity.