AN EFFICIENT AND CONVENIENT SYNTHESIS OF 4,5,6,7-TETRAHYDROTHIENO[3,2-c]PYRIDINES BY A MODIFIED PICTET-SPENGLER REACTION VIA A FORMYLIMINIUM ION INTERMEDIATE

摘要

A synthesis of N-formyl-4,5,6,7-tetrahydrothieno[3,2-c]pyridines was achieved in a highly efficient manner via trifluoroacetic acid catalyzed cyclization of formyliminium ion, which was produced by imination of 2-(2-thienyl)ethylamine and a carbonyl compound using titanium(IV) tetraisopropoxide followed by formylation with acetic-formic anhydride in a one-pot procedure. This modified Pictet-Spengler reaction provides a convenient method for preparing 4,5,6,7-tetahydrothieno[3,2-c]pyridines possessing various substituents at C-4.