Abstract
Indole-2-carboxylic acid and its derivatives (2) are much more stable than usual indoles (1) toward acid and oxidation condition, while still reactive at the 3-position. As the 2-carboxyl group of 2 can easily be removed by decarboxylation, 2 can be considered to be stable equivalent of 1. The expected role of the carboxyl (or ester) group at the 2-position is i) stabilization of the pyrrole ring, ii) to give 2 different reactivities from 1, iii) conversion itself to other functional group, and iv) use as a blocking group. On the basis of this concept reported syntheses, reactivities, and synthetic application of 2 are reviewed.
