Enantioselective Total Synthesis of cis-Trikentrin B

Natural cis -trikentrin B was synthesized enantioselectively using, as key steps, an intramolecular Diels−Alder reaction of an allenic dienamide followed by aromatization to construct an indole ring and cleavage of bicyclo[2.2.1]heptene to launch a cis -dimethylcyclopentane ring. Diels−Alder adducts 9 and 10 were elaborated to provide allenic dienamide 25, and its intramolecular Diels−Alder reaction proceeded smoothly. Aromatization to an indole ring and stereoselective cleavage of the bicyclo[2.2.1]heptene ring were performed successfully. Introduction of an ( E )-butenyl group via addition of propylmagnesium bromide and subsequent anti elimination of water gave natural cis -trikentrin B.