The synthesis and chemical reactivity of thieno[2,3-c]- and thieno[3,2-c] pyridines

The syntheses and reactions of various thieno2,3-c]- and thieno3,2-c] pyridines are described. Molecular orbital calculations were performed on thieno2,3-c]pyridine (1) in order to determine the most susceptible sites to electrophilic and nucleophilic attack. Superdelocalizability values, S_r- are reported for each position in this molecule to give relative orders of reactivity towards the two types of reactions. Electrophilic attack was found to occur experimentally at C-3 in all the thienopyridines studied. Peracid oxidation of thieno2,3-c]- and thieno3,2-c]pyridines produced only the N-oxide. The lack of reactivity of certain thienopyridines under Vilsmeier formylation and Friedel-Crafts acetylation conditions was related to their basicities. The dissociation constants of various thienopyridinium salts are reported.