Radical-mediated synthesis of the 5,11-methanomorphanthridine ring system: formal total synthesis of montanine-type Amaryllidaceae alkaloids, (±)-montanine, (±)-coccinine and (±)-pancracine

Radical-mediated reaction of the phenyl sulfide 16 and the phenyl selenide 17 in boiling toluene or o-xylene containing AIBN gave, in moderate yields, the 5, 11-methanomorphanthridine ring system 4, which is a basic skeleton of montanine-type Amaryllidaceae alkaloids, and formal total synthesis of the title alkaloids 1–3 by conversion of 5, 11-methanomorphanthridin-2-one 5, derived from N-(4-oxocyclohex-2-enyl)-4-phenylthiotetrahydroisoquinoline 21 using this methodology, into the 2,3-benzylidenedioxy-5,11-methanomorphanthridine 31 is achieved.