Facile synthesis of a benzindenoazepine alkaloid, bulgaramine, via samarium diiodide promoted ring expansion of an alpha-aminocarbonyl compound.

A novel synthetic path to a benzindenoazepine alkaloid was established by employing a samarium diiodide promoted ring expansion reaction of an alpha-aminocarbonyl compound as a key reaction, in which a regioselective carbon-nitrogen bond cleavage followed by ring-closing reactions occurred to give the basic ring skeleton of the target compound. Bulgaramine was synthesized from the known tetrahydroisoquinoline derivative in 5 steps in 50% overall yield.