Synthesis and functionalization of indoles through rhodium-catalyzed reactions

Indoles are abundant in nature, and exhibit important biological properties such as anti-inflammatory, anti hypertensive, dopaminergic, antineoplastic, anticonvulsant, analgesic, sedative, muscle relaxant, and antimicrobial activities. Synthesis, and functionalization of pharmacologically active indoles continue to receive considerable attention in the field of synthetic organic chemistry. Recent advances toward synthesis of natural, and unnatural indoles have been accelerated by transition metal catalysts, and in the context rhodium has proven to be an extremely useful metal due to its ability to catalyze an array of synthetic transformations with quite often-unique selectivity. This review describes the formation of indoles via rhodium catalyzed C-H, and X-H insertion (X=N, O, and S), cycloaddition, hydroformylation, bimetallic, and asymmetric hydrogenation reactions. Use of solid phase chemistry in rhodium catalyzed indole synthesis has also been discussed in the article.