A novel annulation reaction of 3-acylmethylidene oxindoles with Huisgen zwitterions is unveiled that leads to an unprecedented synthetic method for complex pyrrolo[4,3,2-de]quinolinones and marine alkaloids ammosamides A–C. This method features simplicity, high efficiency, and broad substrate scope and is accordingly anticipated to significantly facilitate the preparation and bioassay of the relevant pyrroloquinoline alkaloids and their analogues.