A tandem Friedel-Crafts based method for the construction of a tricyclic pyrroloquinoline skeleton and its application in the synthesis of ammosamide B.

A total synthesis of ammosamide B (2), a member of the pyrroloquinoline alkaloid family isolated from marine Streptomyces, is described. The characteristic core tricyclic structure of 2 was constructed using a novel, tandem Friedel-Crafts reaction sequence to transform the symmetric tetra-amino substituted benzene derivative 7 into the tricyclic pyrroloquinoline product 8, which serves as an important intermediate in the route to the synthesis of the target natural product.