Derivatives of a new heterocyclic ring system of [1,2,4]triazolo[5′,1′: 2,3][1,3]thiazino[6,5-b]quinolines (4,5,6,7 and 8) have been synthesised by the reaction of 2-chloroquinoline-3-carbaldehyde derivatives (1 and 2) with 1,2,4-triazole-5-thiols (3), and subsequent transformations of the hydroxy group of 11-hydroxy[1,2,4]triazolo[5′,1′: 2,3][1,3]thiazino[6,5-b]quinoline (4a).