**18. Iminium catalysis: β-alkylation of enals and enones**

A major breakthrough in the field of asymmetric radical chemistry was represented by Melchiorre group; they achieved the first enantioselective radical conjugate addition (RCA) to β,β-disubstituted cyclic enones by a combination of photoredox catalysis and iminium-based organocatalysis. The organocatalyst and the primary amine moiety react with a α,β-unsaturated enone forming a chiral iminium ion as the reactive intermediate; the 1,3-benzodioxole present in the reaction medium upon irradiation by means of an UV light-emitting diode and in the presence of tetrabutylammonium decatungstate (TBADT) generates a carboncentered radical. Thus generated carbon-centered radical being short-lived and active, it reacts with the chiral iminium ion producing an α-iminyl radical cation. Then through an intramolecular SET process, the α-iminyl radical cation was reduced to enamine. A tautomerism reaction, that is, enamine-imine tautomerization, regenerates photocatalyst TBADT, and finally the work procedure gives rise to the product with excellent enantio- and diastereoselectivities, and the chiral amine is recovered [22] (**Figure 24**).

**Figure 24.** *Iminium catalysis: β-alkylation of enals and enones.*
