Synthesis of some pyrimido[1,6-a]benzimidazole derivatives

The base-catalysed condensation of 2-(p-'amihoethyl)benzimidazole (V) with a variety of aldehydes,such as formaldehyde, benzaldehyde, p-chlorobenzaldehyde,etc, yields tetrahydropyrimido-[1,6-a], benzimidazoles (VI). The NMR spectral data of the products decidedly favour a cyclic structure VI as compared to the isomeric open chain Schiff's base (VII). Condensation of carbon disulphide with V affords 3,4-dihydropyrimido[l,6-a]benzimidazole-l(2H)thione (XV). With piperidine and morpholirie, XV yields the thiocarbamoyl derivatives (XVI) of the original amine (V)