Synthesis of novel pentacyclic pyrrolothiazolobenzoquinolinones, analogs of natural marine alkaloids

Multistep synthesis (12 steps) of new pentacyclic compounds, which are structurally very close to natural marine alkaloids, was performed via a Diels–Alder reaction between 4-methylene-5-(bromomethylene)-4,5-dihydrothiazole and a protected dioxotryptamine, itself obtained from the commercially available 2,5-dimethoxybenzaldehyde.