Regioselective indole C2-alkylation using β-CF3-substituted enones under redox neutral Rh(III) catalysis
Rhodium(III) catalyzed C–H alkylation at the C2-position of indole with β-trifluoromethyl-α,β-unsaturated ketones is described. The reactions proceed efficiently with low catalyst loading and a broad range of substrates with excellent functional group compatibility. The scale-up reaction was successfully achieved with 0.5 mol% of the Rh catalyst without significant decrease in the yield. This protocol provides direct access to pharmaceutically important indole derivatives containing a stereogenic carbon center bearing a CF3 functionality at the C2-position.