3,5-Dibenzylidene-1-isopropy1-4-piperidinone (1) reacts with cyanothioacetamide to give 1,6-naphthyridine-2(1H) thione derivative 2. Reaction of 2 with halo ketones or halo esters followed by ring closure gives thieno[2,3-b][1,6]naphthyridine derivatives 5a—i, which are used as versatile intermediates in the synthesis of related heterocyclic ring systems as pyrimidothienonaphthyridines 10, 11, 14, and 15, oxazinothienonaphthyridine (13) and triazinothienonaphthyridine (9).