A micellar catalysis strategy applied to the Pd-catalyzed C-H arylation of indoles in water

The selective control over multiple competing C-H sites would enable straightforward access to functionalized indoles. In this context, we report here a modular and selective C-H arylation of indoles following the micellar catalysis approach using the third generation designer surfactant SPGS-550-M in the presence of 1 mol% of [(cinnamyl)PdCl](2) under mild conditions. Thus, access to high value C-arylated (C-3 and C-2) indoles was achieved fulfilling the triple bottom line philosophy of green chemistry. The nature of the phosphine ligand was found to be critical for achieving site-selectivity, DPPF and DPPP being the most effective in promoting the arylation at C-3-H and C-2-H, respectively. The reaction is scalable and offers high chemo- (C vs. N) and regio-selectivity (C-3 vs. C-2) with a wide range of functional group tolerance. The surfactant aqueous solution can be recycled and reused without compromising on product yields.