Natural isoquinolinium alkaloids possess a wide range of biological activities.The design and synthesis of mesoionic isoquinoliniums is of great importance.This paper reports the synthesis of unique mesoionic thiazoloisoquinolinium thiolates stabilized by aromatization and 1,3-dipolarization.Such compounds can be synthesized via the three component[2 + 2 + 1]cycloaddition reaction of isoquinolines with ethyl propionate and elemental sulfur in the absence of any metal catalyst and additives.Importantly,thiazoloisoquinolinium thiolates can be transformed to thioether-containing thiazoloisoquinolinium halides.A selective[4 + 2]cycloaddition can also be used to form S-bridged fused tetracyclic compounds with a thiothiamide ring unit and two quarternary carbon centres.Compound I-1 shows good bioactivity against the chlorophyll of duckweed (Lemna minor) with inhibition rate of 51.5 μg/mL.