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

By employing [IrCp*Cl ] /Mg(OMe) /(CH O) as an applicable catalyst system, we report a reductive β-alkylation of (iso)quinolinium salts with cost-effective and readily available β-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 a sequence of hydride transfer-initiated dearomatization of (iso)quinolinium salts, 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.