**14. β-Arylation of aldehydes**

The direct β-functionalization of carbonyl groups is very little known. MacMillan et al. first reported the combination of organocatalysis and photoredox catalysis for the direct β-CdH arylation of carbonyl compounds using benzonitrile as aryl donor (**Figure 18**). The proposed mechanistic rationale is shown in **Figure 19** and

**Figure 19.** *β-Arylation of aldehydes—organocatalytic cycle.*

*Visible-Light Photocatalysis of Aldehyde and Carbonyl Functionalities, an Innovative Domain DOI: http://dx.doi.org/10.5772/intechopen.92372*

follows an oxidative quenching cycle pathway, starting with the formation of a cyclohexadienyl radical anion [19].
