Chemistry of thienopyridines. XXXIII. Synthetic routes to 5‐ and 7‐substituted thieno[3,2‐<i>b</i>]pyridines from the <i>N</i>‐oxide

Abstract

Abstract Thieno[3,2‐ b ]pyridine ( 1 ) is oxidized to N ‐oxide 1a by means of m ‐chloroperoxybenzoic acid (83%). Compound 1a forms adducts with hydrogen chloride and picric acid and gives ring substitution alpha or gamma to the heteronitrogen atom. Thus, 1a plus nitric and sulfuric acids produces the 7‐nitro‐ N ‐oxide 1m (63%), or plus phosphorus oxychloride gives a mixture of 5‐chloro and 7‐chloro ( 1j ) derivatives of 1 . Compound 1m is convertible into a variety of other derivatives of 1 , viz . 7‐chloro‐ N ‐oxide, 1j , 7‐bromo‐ N ‐oxide, 7‐nitro and 7‐amino. 5‐Cyano‐ 1 , formed from 1a , is, in turn, transformed into a methyl imidate (93%), cyclic amidines, and a 5‐tetrazolyl‐ 1 (91%). These results confirm the prediction that 1a , thieno[2,3‐ b ]pyridine‐4‐oxide and quinoline 1‐oxide should exhibit closely similar ( i.e. analogous) chemical reactions.