Recent uses of palladium chemistry in indole synthesis

Indoles are extremely important and basic skeletons in many biologically active natural products with specific structures. The development of effective methods for the construction of the indole moiety is one of the most important aims that synthetic chemistry has pursued. Over the past decade, palladium-catalyzed indole synthesis is arguably one of the most successful and straight forward methods for the construction of the pyrrole ring in indole because it offers an efficient entryway from relatively simple precursors with fewer steps, to highly functionalized indoles. This review will summarize recent advances in utilizing this method in the synthesis of most complex indole derivatives such as indolo[2,3-a]carbazoles, optically active 7-methoxytryptophan ethyl esters, pyrimido[4,5-b]indoles and spiro-oxindoles which are present in several biologically important molecules. Also, the use of solid phase chemistry in preparing small libraries of indoles such as two- or three-point diversified complex indole derivatives has been discussed.