Efficient Palladium‐Catalyzed Aerobic Oxidative Carbocyclization to Seven‐Membered Heterocycles

• Published in: Chemistry : a European journal Vol. 26; no. 67; pp. 15513 - 15518
• Main Authors: Liu, Jie, Bäckvall, Jan‐E.
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 01.12.2020; Wiley Subscription Services, Inc; John Wiley and Sons Inc
• Subjects: aerobic oxidation; carbocyclization; Catalysts; Chemical reactions; Chemistry; Chemistry, Multidisciplinary; Communication; Communications; Deactivation; Electron transfer; Functional groups; heterocycles; Hydroquinone; Organic chemistry; Oxidation; Oxygen; Palladium; Physical Sciences; regioseletivity; Reoxidation; Science & Technology; Substrates; KETONES; carbocyclization; regioseletivity; HYDROCARBONS; heterocycles; ARYLATION; MULTISTEP ELECTRON-TRANSFER; palladium; OLEFINS; aerobic oxidation; H BOND FUNCTIONALIZATION; MOLECULAR-OXYGEN
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202004265

The use of molecular oxygen in palladium‐catalyzed oxidation reactions is highly widespread in organic chemistry. However, the direct reoxidation of palladium by O2 is often kinetically unfavored, thus leading the deactivation of the palladium catalyst during the catalytic cycle. In the present work, we report a highly selective palladium‐catalyzed carbocyclization of bisallenes to seven‐membered heterocycles under atmospheric pressure of O2. The use of a homogenous hybrid catalyst (Co(salophen)‐HQ, HQ=hydroquinone) significantly promotes efficient electron transfer between the palladium catalyst and O2 through a low‐energy pathway. This aerobic oxidative transformation shows broad substrate scope and functional group compatibility and allowed the preparation of O‐containing seven‐membered rings in good yields in most cases. Heterocycles: We report a PdII‐catalyzed oxidative carbocyclization of the rationally designed bisallenes using molecular oxygen. By applying a bifunctional catalyst (Co(salophen)‐HQ) as an efficient electron‐transfer mediator, bisallenes are effectively converted to the corresponding seven‐membered carbocycles in good yields (see scheme).