Intramolecular hydrogen bonding in acylated 2,2'bipyridine-3,3'-diamines

Various di- and monoacylated 2,2'-bipyridine-3,3'-diamines (amides 1a-f, 8, 9, ureas 1g-h, 8b and acylureas 1i-j) have been synthesized and characterized. All molecules show strong intramolecular hydrogen bonding between the acyl NH of one ring and the pyridine N-1 of the other (and vice versa), as is deduced from the low field 1H NMR resonances of the acyl NH protons, which range from d 12.6 to 15.0 ppm in CDCl3. The nature of the secondary structure of the (di)acylated 2,2'-bipyridine-3,3'-diamines has been investigated using a variety of techniques including variable-temperature 1H NMR and CD spectroscopy.