Formal total synthesis of histrionicotoxin alkaloids via Hg(OTf) 2 -catalyzed cycloisomerization and SmI 2 -induced ring expansion.

The efficient formal total synthesis of histrionicotoxin alkaloids was achieved. In this process, two key reactions were used to construct a core 1-azaspiro[5.5]undecane framework common to histrionicotoxins: a mercuric triflate (Hg(OTf) 2 )-catalyzed cycloisomerization of a linear substrate, which was developed in our laboratory, and a samarium iodide (SmI 2 )-mediated ring expansion.