Regioselective synthesis of the novel 7-hydroxy-2-(alkylsulfanyl)-6-undecyl[1,3,4]thiadiazolo[3,2- a]benzimidazole-5,8-diones was achieved by the reaction of 2,5-dihydroxy-6-undecyl-1,4-bezoquinone (embelin) with 5-(alkyl/aralkyl/ phenacylsulfanyl)-1,3,4-thiadiazol-2-amines in refluxing acetic acid.