Iridium-catalyzed reductive β-alkylation of (iso)quinoline derivatives by an in situ enone-trapping strategy

By employing [IrCp*Cl-2](2)/Mg(OMe)(2)/(CH2O)n as an applicable catalyst system, we report a reductive beta-alkylation of (iso)quinolinium salts with cost-effective and readily available beta-chloro ketones, proceeding with good chemoselectivity, mild reaction conditions, and without the need for introduction of a substituent at position-3 of the quinolyl skeleton. Mechanistic investigations suggest that the reaction proceeds via a sequence of hydride transfer-initiated dearomatization of (iso)quinolinium salts, in situ enamine-trapping of enone and a second round of hydride transfer to the coupling adducts. The present work offers an important complement to the synthesis of functionalized (iso)tetrahydroquinolines.