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.
Keywords: carbinol anions; carbon dioxide; cross-pinacol coupling; photocatalysis; umpolung.
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