Chemistry of thienopyridines. XVIII. Lithiation as a route to 2‐ and 3‐substituted thieno[2,3‐b]pyridines

Treatment of thieno[2,3‐b]pyridine (1a) with n‐butyllithium in hexane‐tetramethylethylene‐diamine at −70° plus subsequent addition of dimethylformamide produced 2‐formyl‐Ia (66%). Halogen‐metal exchange between 3‐bromothieno[2,3‐b]pyridine and n‐butyllithium was effected in ether at −70. Further reaction of the 3‐lithio‐Ia intermediate with a variety of carbonyl compounds gave 3‐substituted thieno[2,3‐b]pyridines bearing formyl (77%), acetyl, benzoyl, chloroacetyl, ethoxycarbonyl, N‐phenylcarbamyl, and diphenyl hydroxymethyl groups. Common characteristics of these derivatives in pmr and mass spectra are noted.