The synthesis of new tricyclic derivatives having sulfur-containing six or
seven-membered rings fused to the <<a>> edge of benzimidazole system, is re
ported. The stereochemical characteristics of thiazino- and thiazepinobenzi
midazoles (4-7) are described and comparative NMR data are discussed. The s
ynthetic approach to new benzo- or pyridothiazinobenzimidazole tetracyclic
systems (8) is also reported.