Metal‐Free CH Bond Activation of Branched Aldehydes with a Hypervalent Iodine(III) Catalyst under Visible‐Light Photolysis: Successful Trapping with Electron‐Deficient Olefins

Abstract

Direct acyl radical formation of linear aldehydes (RCH2-CHO) and subsequent hydroacylation with electron-deficient olefins can be effected with various types of metal and nonmetal catalysts/reagents. In marked contrast, however, no successful reports on the use of branched aldehydes have been made thus far because of their strong tendency of generating alkyl radicals through the facile decarbonylation of acyl radicals. Here, use of a hypervalent iodine(III) catalyst under visible light photolysis allows a mild way of generating acyl radicals from various branched aldehydes, thereby giving the corresponding hydroacylated products almost exclusively. Another characteristic feature of this approach is the catalytic use of hypervalent iodine(III) reagent, which is a rare example on the generation of radicals in hypervalent iodine chemistry.

Sunlight‐Driven Decarboxylative Alkynylation of α‐Keto Acids with Bromoacetylenes by Hypervalent Iodine Reagent Catalysis: A Facile Approach to Ynones

“…Based on the preliminary study, a possible mechanism for the reaction is proposed in Scheme . Firstly, BI‐OH reacts with 2‐oxo‐2‐phenylacetic acid ( 1 a ) to form the intermediate 5 ,15 and is initiated by sunlight irradiation to generate the iodanyl radical A 9e, 16 and acyl radical B . Next, A reacts with 2 a to give BI‐Alkyne and a Br radical.…”

Green Photo‐Organocatalytic C−H Activation of Aldehydes: Selective Hydroacylation of Electron‐Deficient Alkenes

“…The best solution was given by Maruoka and co‐workers by employing a hypervalent iodine compound as a photoinitiator . Maruoka and co‐workers identified the optimum hypervalent iodine compound to promote this reaction with excellent selectivity towards the acyl radical, studied the reaction mechanism, and provided a diastereoselective method . Unfortunately, the catalyst is not commercially available.…”

Recent Advances in Photoredox Methods for Ketone Synthesis

“…In 2014, Maruoka and co‐workers came forward with a photocatalytic method for generating acyl radicals from branched chain aldehydes using hypervalent iodine(III) catalysts (Scheme ) . Notably, generating branched acyl radicals is very difficult as they are prone to undergo decarbonylation to form more stable alkyl radicals thereby leading to formation of alkylated products instead.…”