ChemInform Abstract: Reactions of Pyrido(1,2‐a)benzimidazole (I).

Crowded Piperidines with Intramolecularly Hydrogen-Bonded Nitrogen: Synthesis and Conformation Study

“…In the 1 H NMR spectrum of piperidone 15 we can detect a long‐range coupling interaction between the axial protons H‐3 and H‐5 (2.4 Hz), which, being diastereotopic, are chemically nonequivalent. Cyclic ketones only possess such a long‐range spin–spin interaction in the chair conformation 2d. In addition, the chemical shift difference for the geminal protons in the 3‐ and 5‐positions of 17 (0.48 ppm) is the same as the difference for the equatorial and axial protons at C‐2 of the conformationally restricted “chair compound” 16 (0.46 ppm).…”

Reaction of substituted pyrido[1,2-a]benzimidazoles with electrophilic agents

“…Nitration of nonsubstituted pyrido[1,2-a]benzimidazoles and benzimidazo[1,2-a]quinolines have been reported to also occurr at position 8. [20][21][22][23] The low yield of product 2c (49%) could be explained by partial hydrolysis of the cyano group and formation of a mixture of compounds (2c, 2d). Separation of these compounds was carried out by heating in a 2:1 isopropanol-DMF solution at reflux in which nitrile 2c was insoluble.…”