Ketones were selectively synthesized from thioesters by using diarylcuprates(I) generated in situ from copper(I) salts and aryl Grignard reagents in a 1 : 1.3–1.5 ratio under ambient temperature. During the ketone synthesis, various functional groups, such as carbonyl (ketones, esters, and amides), O‐protecting groups, halogens, and heteroarenes, were tolerated to afford multifunctionalized ketones in excellent yields. This copper‐mediated ketone synthesis could be applied to the synthesis of not only gluconolactone‐derived ketone 6, a synthetic intermediate in the transformation to the SGLT2 inhibitor canagliflozin, but also thiolactol 8, a valuable synthetic intermediate for (+)‐biotin. Control experiments on an isolated diphenylcuprate(I), [CuPh2]− (12), and DFT calculations revealed that this ketone synthesis proceeded by oxidative addition of the C−S bond of thioesters to [CuPh2]−, while reductive elimination from the CuIII intermediate produced the corresponding ketone and an inactive species [(RS)CuPh]−, the latter reacted with [CuPh]4 (11) to regenerate the reactive diphenylcuprate(I).

The synthesis of ketone as a synthetic intermediate of canagliflozin from a gluconolactone‐derived thioester and a Grignard reagent with the aid of copper is likened to making Taiyaki, a Japanese fish‐shaped waffle with sweet red bean inside. The thioester (sweet red beans) and the Grignard reagent (waffle batter) are baked on a copper waffle iron to get the desired ketone as Taiyaki. More information can be found in the Research Article by H. Tsurugi, M. Seki, K. Mashima, and co‐workers (DOI: 10.1002/chem.202200474).