Total syntheses of the marine sponge pigments fascaplysin and homofascaplysin B and C
作者:Gordon W. Gribble、Benjamin Pelcman
DOI:10.1021/jo00039a024
日期:1992.6
The Fascaplysinopsis spp. marine sponge pigments fascaplysin (1), homofascaplysin B (4), and homofascaplysin C (5) have been synthesized by peracid oxidation, reaction with oxalyl chloride/methanol, or Vilsmeier formylation, respectively, of the keystone intermediate 12H-pyrido[1,2-a:3,4-b']diindole (7). The versatile 7 was prepared from indole (17) in six steps (78% yield), a sequence in which the key reaction is the trifluoroacetic acid-induced ring closure of diindole 15, followed by Pd/C-catalyzed dehydrogenation of the crude mixture of cyclized products 25, 26, to give 7 in 93% yield from 15.