LOW-VALENT TITANIUM INDUCED INDOLE FORMATION - SYNTHESES OF SECOFASCAPLYSIN, INDOLOPYRIDOCOLINE AND AN ENDOTHELIN-RECEPTOR-ANTAGONIST

The versatility of a titanium-induced reductive oxo-amide coupling rea ction is illustrated by the syntheses of the alkaloids secofascaplysin 8 and indolopyridocoline 14 as well as by an efficient and flexible a pproach to the arylated indole-2-carboxylic acid 4, which has recently been disclosed as a promising endothelin-receptor-antagonist. Dependi ng on the particular substitution pattern in the substrates, either pr e-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. Copyright (C) 1996 Elsevier Scien ce Ltd