Total syntheses of five indole alkaloids from the marine bryozoan Flustra foliacea

A general, efficient, and conceptually new approach to the total syntheses of marine-derived indole alkaloids, including (+/-)-flustramines A (I) and B (2), (+/-)-flustramides A (3) and B (4), and (+/-)-debromoflustramine B ( 5), is outlined. The key step in the syntheses involves the conjugated addi tion of an organomagnesium species derived from prenyl bromide to 2-hydroxy indolenines. Compounds 1. 2, and 5 have been synthesized in five steps with 23%, 17%, and 16% overall yield, respectively, whereas flustramides 3 and 4 have been synthesized in only four steps with 24% and 18% overall yield, respectively, on the basis of 2-hydroxyindolenines.