Synthesis of the First Representatives of Thieno[3,2-c][1,7]naphthyridine Derivatives Based on 3-Amino-6-methyl-4-(2-thienyl)pyridin-2(1H )-one

A one-pot method for obtaining novel thieno[3,2c][ 1,7] naphthyridine derivatives based on the reaction of 3-amino-4( thien-2-yl)pyridin-2(1H)-one with aromatic aldehydes in 80% phosphoric acid at 130 degrees C has been developed. The formation of the thieno[3,2-c][1,7] naphthyridine ring was due to the intermediate generation of the corresponding azomethine, which underwent intramolecular cyclization with electrophilic attack of the beta-carbon atom of the thiophene core under Pictet-Spengler conditions. The isolated 5,7-dihydrothieno[ 3,2-c][1,7]naphthyridin-4(3H)-ones underwent oxidative aromatization in air to give thieno[3,2-c][1,7] naphthyridin-6(7H)ones. A two-step synthesis of thieno[3,2-c][1,7] naphthyridines involving the isolation of the intermediate imine did not lead to a significant increase in the product yield.