Copper-Catalyzed Synthesis of Indole-2-carboxylates

Significance

Reported is the straightforward synthesis of indole-2-carboxylate derivatives 3 from the reaction of 2-halo aryl aldehydes or ketones 1 with ethyl isocyanoacetate 2 under ligand-free copper(I) catalysis. The reaction proceeds at room temperature (for X = I) or elevated temperature (for X = Cl, Br) and is tolerant of both EDG and EWG on the aromatic ring. In general, higher yields were observed from ketone substrates compared to the aldehydes. The reaction was extended to the synthesis of 7-azaindole 4 and the unusual thienopyrroles 5 and 6 in good yield.