Synthesis of 4-Aryl-1,7-naphthyridine-2(1H)-thiones by the Electrocyclic Reaction of 4-(1-Arylalk-1-enyl)-3-isothiocyanatopyridines Generated in situ from the Corresponding Isocyanides

A convenient synthis for 4-substituted and 3,4-disubstituted 1,7-naphthyridine-2(1H)-thiones 7 has been developed. The method is based on the electrocyclic reaction of 4-(1-arylalk-1-enyl)-3-isothiocyanatopyridines 6, generated in situ by the treatment of the respective isocyanides 5 with S8 in the presence of a catalytic amount of selenium. The isocyanides 5 can be easily prepared from commercially available pyridin-3-amine by conventional organic reactions.