Iridium-Catalyzed Heteroannulation Route to Benzofurans and Indoles

Significance

Previous studies on the rhodium- and iridium-catalyzed C-H activation of aryl ­ketones form the basis of the reported directed cyclodehydration route of α-aryloxy and α-aryl­amino ketones to benzofuran derivatives. After screening conditions, rhodium was found to be ineffective, but the [Ir(cod)₂]BARF complex afforded the corresponding 4-substituted benzofurans and indoles in high yields. Esters, amides, and the acetyl group were found to be applicable as directing group (DG) in the reaction, albeit only one example is provided for esters and amides. The regioselectivity is presumably driven by iridium coordination of DG and the incipient carbonyl involved in the cyclodehydration step. Interestingly, chiral BINAP was successfully applied in the reaction to afford a chiral oxindole with moderate enantioselectivity.