Low-valent titanium induced indole formation: Syntheses of secofascaplysin, indolopyridocoline and an endothelin-receptor-antagonist

Article abstract of DOI:10.1016/0040-4020(96)00255-4

The versatility of a titanium-induced reductive oxo-amide coupling reaction is illustrated by the syntheses of the alkaloids secofrascaplysin 8 and indolopyridocoline 14 as well as by an efficient and flexible approach to the arylated indole-2-carboxylic acid 4, which has recently been disclosed as a promising endothelin-receptor-antagonist. Depending on the particular substitution pattern in the substrates, either pre-formed titanium on graphite or low-valent titanium formed in situ ('instant conditions') are the preferred coupling agents for reductive heterocycle syntheses of this type.