2,4-Substituted quinolines of type I [R = CH(OEt)2, CHO, R1 = 3,4,5-(MeO)3C6H2, 4-MeO2CC6H4, CF3, Ph, 3,5-(MeO)2C6H3, 3,4-(MeO)2C6H3] were synthesized starting from 2-aminothiophenol and acetylenic acetals R1COCCCH(OEt)2 to yield various substituted benzo[b][1,4]thiazepine intermediates of type II. Subsequent sulfur extrusion in refluxing toluene led to 2,4-substituted quinoline acetals I [R = CH(OEt)2], which were transformed into the corresponding 2-substituted quinoline-4-carbaldehydes I (R = CHO) in good to excellent yields.