Photocatalytic Cross‐Pinacol Coupling Promoted by Carbon Dioxide**

Abstract

Cross‐pinacol coupling of two different carbonyl compounds was achieved through successive one‐electron transfer processes under photocatalytic conditions. In the reaction, an umpoled anionic carbinol synthon was generated in situ to react nucleophilically with a second electrophilic carbonyl compound. It was revealed that a CO2 additive promoted the photocatalytic generation of the carbinol synthon to suppress undesired radical dimerization. A wide variety of aromatic and aliphatic carbonyl substrates underwent the cross‐pinacol coupling to afford the corresponding unsymmetric vicinal 1,2‐diols, in which even a combination of carbonyl reactants with similar structures such as two aldehydes and two ketones were also well tolerated with high cross‐coupling selectivity.

CO2 and palladium enabled highly chemoselective hydroxylation of gem-difluorocyclopropanes

“…Moreover, we characterized the nucleophile activating role of CO 2 through key mechanistic experiments. The herein presented results should encourage the development of further challenging coupling reactions with weak X–H nucleophiles such as water, by means of CO 2 catalysis, 74–77 and in general the use of CO 2 in synthetic method development. 78…”

Visible-Light-Antenna Ligand-Enabled Samarium-Catalyzed Reductive Transformations

“…The acetaldehyde, generated in situ, supports the hydrolysis of the iminium cation of DIPEA (Figure f). The cross-pinacol coupling product 4a probably resulted from the nucleophilic addition of the benzylic carbanion of 3a to acetaldehyde . This observation suggests that the Sm/DPA-1 catalytic system enabled the two-time single-electron reduction of 3a , generating a benzylic carbanion stabilized by the 2-pyridyl group.…”

Photoredox catalyzed release of carbon-based radicals from 2-substituted-1,3-imidazolidines

“…9 To strengthen the reducing power of compounds I the process was later promoted by light via a photoinduced electron transfer reaction (Scheme 1). 10 Interestingly, aminals I may also act as efficient hydrogen atom donors to radicals ( e.g. V , path d) 9 More recently, even radical III has found application as a surrogate of an acyl radical VI in the reaction with styrenes.…”