Preparation of new nitrogen-bridged heterocycles 72. A new approach to 1-acyl-3-(substituted methylthio)thieno[3′,4′:4,5]imidazo[1,5-a]- pyridine derivatives

摘要

The alkaline treatment of the pyridinium salts, readily available from the S-alkylations of 3-amino-4-(1-pyridinio) thiophene-5-thiolates with various alkyl halides, in chloroform at room temperature afforded the corresponding thieno[3′,4′:4,5]imidazo[1,2-a]pyridine derivatives in low to moderate yields via the intramolecular cyclization of the resulting 1,5-dipoles followed by the aromatization of the primary cycloadducts. Interestingly, the reactions using unsymmetrical 3-amino-4-[1-(3-methylpyridinio)]thiophene-5- thiolates afforded only 8-methylthieno[3′,4′:4,5]imidazo[1,2-a] pyridines and the other 6-methyl derivatives were not formed at all. In addition the isolation of a byproduct in the condensation reaction of pyridinium salt with the solvent (CHCl_3) is also discussed.