Heterocycles of biological importance. Part 5. The formation of novel biologically active pyrimido[1,2-a]benzimidazoles from allenic nitriles and aminobenzimidazoles

摘要

The reaction of allenic nitriles with 2-aminobenzimidazoles gives 2-aminopyrimido[1,2-a]benzimidazoles 5 in veryngood yields. The pharmacological screening of compound 5a, 5d and 5i shows that they possess slight antibiotic andnantiarrythmic properties.nThe usefulness of allenic nitriles as starting materials in heterocyclicnsyntheses has been clearly demonstrated.2–12 As a continuationnof that work, we decided to study the synthesis andnbiological activity of heterocycles that could be readilynobtained by the reaction of various substituents with allenicnand acetylenic nitriles.13–15 In this paper, we report the reactionnof substituted or unsubstituted aminobenzimidazoles 1 withnnitriles 2 to give pyrimidobenzimidazoles 5 that possess somenbiological activity. The allenic nitriles 2 were treated with aminobenzimidazolesn1 under reflux in N,N-dimethylformamide forn3–4 days, the reaction being monitored by TLC. When thenreaction was stopped after 36 hours, spectral data showed thatntraces of the starting materials, unconjugated enaminic nitrilen3, traces of conjugated enaminic nitrile 4 and some of thenpyrimidobenzimidazole 5 were in the mixture. However, after 4ndays of reaction, all the starting materials had been used up andnthe intermediate enaminic nitriles converted to the final productnin near quantitative yield. When the reaction was carried outnin ethanol for 3 days, the unconjugated adduct 3 was the solenproduct.