Visible‐Light Photoredox‐Catalyzed and Copper‐Promoted Trifluoromethoxylation of Arenediazonium Tetrafluoroborates

Abstract

We report the development of photoredox-catalyzed and copper-promoted trifluoromethoxylation of arenediazonium tetrafluoroborates,w ith trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent. This new method takes advantage of visible-light photoredoxc atalysis to generate the aryl radical under mild conditions,c ombined with copper-promoted selective trifluoromethoxylation. The reaction is scalable,tolerates awide range of functional groups, and proceeds regioselectively under mild reaction conditions. Furthermore,m echanistic studies suggested that aC s[Cu-(OCF 3 ) 2 ]intermediate might be generated during the reaction. Scheme 1. Photoredox-catalyzed and copper-promoted trifluoromethoxylation of arenediazonium tetrafluoroborates.

Aryldiazonium Salts in Photoredox Catalysis – Recent Trends

“…In 2015, Shaoqiang Yang et al converted aryl diazonium salts to aryl trifluoromethoxylated products using dual copper-photoredox catalysis under mild conditions (Scheme 55). [88] They investigated the scope of various aryldiazonium salts containing electron withdrawing, and electron donating substituents. In all cases, the resultant products were obtained in good yields except for ortho-substituted diazonium salts, which afforded the desired product in very low yields under the reaction conditions.…”

Radical α-Trifluoromethoxylation of Ketones under Batch and Flow Conditions by Means of Organic Photoredox Catalysis

“… 13 Under photoredox conditions, these three reagents proved to be efficient for the catalytic C–H trifluoromethoxylation of arenes and heteroarenes. 14 To date, their scope has not been extended beyond (hetero)aromatic substrates. This represents an unprecedented challenge, the success of which would provide access to new or hitherto poorly described molecules due to their cumbersome synthesis.…”

Photocatalytic trifluoromethoxylation of arenes and heteroarenes in continuous-flow

“…Similar results were obtained with carbonyl-containing com-pounds. Different aromatic ketones, aldehydes, esters, and carboxylic acids were transformed to the corresponding trifluoromethoxylated compounds (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) with generally good to high yields, except for 13, 16, 19 and 22 which were obtained in moderate or poor yields. Other synthetically useful substituents, including cyano, nitro, phenylsulphonyl, (pinacolato)boron, and alkyl groups could be tolerated in the reaction (24)(25)(26)(27)(28)(29)(30), leading to a yield range between 26 and 65%.…”

“…These procedures typically required harsh conditions and the use of aggressive and toxic chemicals like BF 3 , HF, MoF 6 , SF 4 , and SbF 3 [10]. Alternative approaches were recently reported [8,9,11], for example the trifluoromethylation of hydroxyaryls [12][13][14], and the direct introduction of the -OCF 3 moiety into an organometallic species [15], a diazo compound [16,17], or an unfunctionalized C-H bond (Scheme 1B). The latter method is particularly interesting, partially due to the general interest of the community into C-H functionalization methodologies [18,19], and partially thanks to the synthetic possibilities enabled by photoredox catalysis, a field widely explored in recent years [20][21][22].…”