Aromatic nitrogen bridgehead compounds. II. The synthesis of 1-Acylmethyl-2-(2-pyridyl)pyridinium salts and their cyclization to 6-substituted Dipyrido[1,2-c:2',1'-e]imidazolium salts

The interaction of 2,2'-bipyridyl, 4,4'-dimethyl-2,2'-bipyridyl, 5,5'-dimethyl- 2,2'-bipyridyl, or l,l0-phenanthroline with aromatic or aliphatic a-haloketones, or with ethyl bromoacetate, gives high yields of 1-acylmethyl-2-(pyridyl)pyridinium salts. These salts can be converted in good yields into 6-substituted dipyrido-[1,2-c:2',1?-e]imidazolium salts by treatment with either bromine and pyridine or p-toluenesulphonyl chloride and pyridine. The mechanisms of these cyclizations are considered.