Conformational Studies of Annulated 2,2′-Bipyridinium Salts

The synthesis of several 4,4′-disubstituted 2,2′-bipyridinium bridged diquaternary salts, by reaction of the corresponding 2,2′-bipyridines with several dibromide substrates, is reported. Further sulfonation of two of these salts gives rise to bridged 2,2′-bipyridines with zwitterionic character, 4a,b. The twist angle between the two pyridine rings can be estimated from spectroscopic data of these salts. In a propane-bridged salt, 9b, a barrier to conformational mobility of 16.5 kcal mol-1has been obtained by a variable-temperature NMR experiment. © 1987, American Chemical Society. All rights reserved.