Abstract The cytotoxic isoquinoline quinone perfragilin B (2), which was isolated from the bryozoan Membranipora perfragilis, has been synthesized. The key step involves a Diels- Alder reaction between a substituted 2-azabutadiene (4) and 2, 3-bis (thiomethyl)-1, 4- benzoquinone (6) to produce the isoquinoline skeleton.
