Friedel-Crafts Alkylation of Indoles via Combinatorial Transition-Metal Catalysis

Significance

Combinatorial transition-metal ­catalysis has recently gained attention as a useful method to enhance the selectivities of many ­organic transformations (see Review below). By mixing ligands (L^a + L^b) with the central metal (M), structurally diverse heterocombinatorial catalysts (ML^aL^b) can be obtained. If this catalyst is more reactive and selective than the corresponding ­homocombinatorial catalysts (ML^aL^a or ML^bL^b), an improved catalyst system is developed without the need of synthesizing new ligands. By applying this principle, the authors have reported a highly enantioselective Friedel-Crafts alkylation of ­indoles with nitroalkenes using the Schiff base L/Zn(II) complex as catalyst and piperidine as ­crucial combinatorial ligand.

Review: M. T. Reetz Angew. Chem. Int. Ed. 2008, 47, 2556-2588.