Palladium(II)‐Catalyzed 1,4‐Addition of Arylboronic Acids to β‐Arylenones for Enantioselective Synthesis of 4‐Aryl‐4H‐chromenes

The enantioselective 1,4‐addition of arylboronic acids to β‐arylenones to give β‐diaryl ketones was carried out at 0–25 °C in the presence of a dicationic palladium(II) catalyst, [Pd( S,S ‐chiraphos)(PhCN) 2 ](SbF 6 ) 2 . Addition of a silver salt such as silver tetrafluoroborate [AgBF 4 ] or silver hexafluoroantimonate [AgSbF 6 ] (5–10 mol %) was effective to achieve high enantioselectivities at low temperatures (92–99 % ee ) and to reduce the catalyst loading to 0.05 mol %. The protocol provided a simple access to 4‐aryl‐4 H ‐chromenes. Optically active chromenes were synthesized with up to 99 % ee via dehydration of the 1,4‐adducts between arylboronic acids and β‐(2‐hydroxyaryl)‐α,β‐unsaturated ketones.