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Photoredox Activation for the Direct β-Arylation of Ketones and Aldehydes

Science  29 Mar 2013:
Vol. 339, Issue 6127, pp. 1593-1596
DOI: 10.1126/science.1232993

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Beta Bonding

Carbonyl compounds, which incorporate carbon-oxygen double bonds, are among the most productively reactive molecules in synthetic as well as biochemical contexts. The carbon directly bonded to oxygen is rendered highly electrophilic, while the adjacent (α) carbons are easily deprotonated to undergo further transformations. In contrast, the β carbons that are one step further along the chain tend to be relatively inert. Pirnot et al. (p. 1593) now show that a dual catalyst system—consisting of an amine and a photoactive metal complex—can activate the β carbons of carbonyl compounds to couple with aryl substrates.

Abstract

The direct β-activation of saturated aldehydes and ketones has long been an elusive transformation. We found that photoredox catalysis in combination with organocatalysis can lead to the transient generation of 5π-electron β-enaminyl radicals from ketones and aldehydes that rapidly couple with cyano-substituted aryl rings at the carbonyl β-position. This mode of activation is suitable for a broad range of carbonyl β-functionalization reactions and is amenable to enantioselective catalysis.

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