Total Synthesis of (-)-Colombiasin and
(-)-Elisapterosin B

Key words

[4+2] cycloaddition - [5+2] cycloaddition - diterpenes - Moore rearrangement

Significance

The target molecules were isolated from the gorgonian octocoral Pseudopterogorgia elisabethae. Elisapterosin B is active against Plasmodium falciparum, the parasite associated with malaria. Two of the three stereogenic centers in D were derived from (-)-dihydrocarvone; the third was generated by hydroboration with Ipc₂BH. All remaining stereogenic centers were created by substrate-controlled processes.

Comment

A very economical synthesis of the target molecules was achieved using a sequence of pericyclic reactions. Hydroquinone D, generated by a Moore rearrangement of the cyclobutenone A, underwent a thermal [4+2] cycloaddition to give Colombiasin A and a Lewis-acid-catalyzed [5+2] cycloaddition on treatment with BF₃·OEt₂ to give Elisapterosin B.