Feng Y, Majireck MM, Weinreb SM * The Pennsylvania State University, University Park,
USA
Total Synthesis of the Unusual Monoterpenoid Indole Alkaloid (±)-Alstilobanine A.
Angew. Chem. Int. Ed. 2012;
51: 12846-12849
Key words
alstilobanine A - nitrosoalkenes - [2+2] cycloaddition - alkaloids - β-lactones
Significance
Monoterpene indole alkaloids usually consist of a tryptamine residue attached to a
monoterpenoid unit. (±)-Alstilobanine A, however, features an intriguing rearranged
skeleton. The authors based their concise synthesis on the conjugate addition of ester
enolate F to an in situ-generated nitrosoalkene and the formation of β-lactam L via an intramolecular formal ketene–ketone [2+2] cycloaddition developed by Romo and
co-workers (Org. Lett.
2006, 8, 4363).
Comment
The intermolecular conjugate addition of ester enolate F onto nitrosoalkene G, generated in situ from α-chlorooxime E, proceeded efficiently to give H. This transformation highlights an interesting method to construct 1,4-dicarbonyl
frameworks. Both C16-diastereomers could be used to access I, which then underwent a formal [2+2] cycloaddition to afford the desired syn-2-azadecalin L in excellent yield and diastereoselectivity. The synthesis was completed in eight
steps from L to generate the natural product in an impressive 14% overall yield.
