Activation of CH Bonds through Oxidant‐Free Photoredox Catalysis: Cross‐Coupling Hydrogen‐Evolution Transformation of Isochromans and β‐Keto Esters. Issue 50 (30th October 2015)

• Record Type: Journal Article
• Authors: Xiang, Ming; Meng, Qing‐Yuan; Li, Jia‐Xin; Zheng, Yi‐Wen; Ye, Chen; Li, Zhi‐Jun; Chen, Bin; Tung, Chen‐Ho; Wu, Li‐Zhu
• Is Part Of: Chemistry. Volume 21:Issue 50(2015)
• Page Start: 18080
• Page End: 18084
• Publication Date: 2015-10-30
• Subjects: CH activation -- isochromans -- oxonium -- photoredox catalysis; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201503361
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The direct and controlled activation of a C(sp 3 )H bond adjacent to an O atom is of particular synthetic value for the conventional derivatization of ethers or alcohols. In general, stoichiometric amounts of an oxidant are required to remove an electron and a hydrogen atom of the ether for subsequent transformations. Herein, we demonstrate that the activation of a CH bond next to an O atom could be achieved under oxidant‐free conditions through photoredox‐neutral catalysis. By using a commercial dyad photosensitizer (Acr + ‐Mes ClO4 −, 9‐mesityl‐10‐methylacridinium perchlorate) and an easily available cobaloxime complex (Co(dmgBF2 )2 ⋅2 MeCN, dmg=dimethylglyoxime), the nucleophilic addition of β‐keto esters to oxonium species, which is rarely observed in photocatalysis, leads to the corresponding coupling products and H2 in moderate to good yields under visible‐light irradiation. Mechanistic studies suggest that both isochroman and the cobaloxime complex quench the electron‐transfer state of this dyad photosensitizer and that benzylic CH bond cleavage is probably the rate‐determining step of this cross‐coupling hydrogen‐evolution transformation. Abstract : H2 evolution : The direct functionalization of a C(sp 3 )H bond adjacent to an O atom is a powerful tool for the conventional derivatization of ethers. The addition of β‐keto esters to oxonium species, which is rarely observed in photocatalysis, proceeds under oxidant‐free conditions by merging a commercial dyad photosensitizer and an easily available cobaloxime complex (see scheme; SET=single‐electron transfer).