5-Methyl-(4a), 7-methyl-(4b), and 8-methyl-5, 6, 7, 8-tetrahydro-1, 6-naphthyridine (4c) were synthesized by chemical modification of pyridine derivatives. On the other hand, the synthesis of the compounds (20b, c) having a methyl group in the aromatic ring of 5, 6, 7, 8-tetrahydro-1, 6-naphthyridine was accomplished by the condensation of 1-benzyl-4-piperidinone with the corresponding 3-amino-enones followed by debenzylation. The pathway of the condensation is briefly discussed.