8H-Isoquino[2,1-b][2,7]naphthyridin-8-ones: synthesis of the Alangium alkaloids, alangimaridine and alangimarine

It is shown that 3,4-dihydroisoquinolines are activated toward nucleophilic attack by reaction with trimethylsilyl trifluoromethanesulfonate. The complex so formed reacts readily with the lithio derivative of 3-cyano-4-methyl-5-vinylpyridine, affording in a single step a tetracyclic amidine from which a lactam is obtained by hydrolysis. These reactions have been applied to the synthesis of the Alangium alkaloids, (±)-alangimaridine and alangimarine.