The 8H-thieno[2,3-b]pyrrolizinones, some of which exert very potent cytotoxic activity against tumor cell lines in vitro, are a promising novel series of anti-cancer agents. These compounds belong to the tripentone family and are based on 9H-pyrrolo[1,2-a]indol-9-one derivatives and their heterocyclic isosteres. This paper inventories the different synthetic strategies for tripentones and reviews their biological effects and therapeutic potential.