**7. Reaction of chiral enamine with α-bromocarbonyl compounds**

Photoredox catalysis and organocatalysis are two powerful fields of molecule activation that have found widespread application in the areas of inorganic coordination and organic chemistry. The merger of these two fields is an important solution in asymmetric chemical synthesis. Specifically, the enantioselective intermolecular α-alkylation of aldehydes with α-bromocarbonyls has been accomplished using an activation pathway that combines both the photoredox catalyst Ru (bpy)3Cl2 (where bpy is 2,2<sup>0</sup> -bipyridine) and an imidazolidinone organocatalyst. This simple alkylation reaction, which was previously elusive, is now broadly applicable and highly enantioselective [11].

The initiation of the reaction requires quenching of the photocatalyst excited state \*Ru(bpy)32+ by a sacrificial amount of enamine to provide the strongly reducing Ru(bpy)3 + . Electron transfer to the alkyl bromide induces fragmentation, affording bromide and the electron-deficient radical. Condensation of the aldehyde with the imidazolidinone organocatalyst furnishes chiral enamine. The CdC bond formation then occurs by the radical electrophile addition to the accessible *Si* face of the enamine and generates the α-amino radical. The two catalytic cycles then intersect with the single-electron oxidation of \* Ru(bpy)3 2+ to yield Ru(bpy)3 <sup>+</sup> and the iminium ion. Hydrolysis of the iminium releases the α-alkylated product and regenerates the organocatalyst (**Figures 10** and **11**).

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

#### **Figure 10.**

range of perfluoroalkyl halides were found to participate in the enantioselective alkylation reaction. N-perfluoroalkyl substrates of varying chain length undergo successfully reductive radical formation and enamine addition with high yields and

*Photophysics, Photochemical and Substitution Reactions - Recent Advances*

**7. Reaction of chiral enamine with α-bromocarbonyl compounds**

This simple alkylation reaction, which was previously elusive, is now broadly

The initiation of the reaction requires quenching of the photocatalyst excited state \*Ru(bpy)32+ by a sacrificial amount of enamine to provide the strongly reduc-

affording bromide and the electron-deficient radical. Condensation of the aldehyde with the imidazolidinone organocatalyst furnishes chiral enamine. The CdC bond formation then occurs by the radical electrophile addition to the accessible *Si* face of the enamine and generates the α-amino radical. The two catalytic cycles then

the iminium ion. Hydrolysis of the iminium releases the α-alkylated product and

. Electron transfer to the alkyl bromide induces fragmentation,

Photoredox catalysis and organocatalysis are two powerful fields of molecule activation that have found widespread application in the areas of inorganic coordination and organic chemistry. The merger of these two fields is an important solution in asymmetric chemical synthesis. Specifically, the enantioselective intermolecular α-alkylation of aldehydes with α-bromocarbonyls has been accomplished using an activation pathway that combines both the photoredox catalyst Ru


Ru(bpy)3

2+ to yield Ru(bpy)3

<sup>+</sup> and

The α-alkylation of carbonyl compounds is always an essential tool in the synthetic organic chemistry. It can be carried out both inter- and intramolecularly; the intramolecular version builds up the cyclic compounds with enhanced stereoselectivity. Among the α-alkylation reactions, of late, α-trifluoromethylation reactions are being much exploited since these compounds are of greater importance in agrochemical and pharmaceutical compounds. Iodotrifluoromethane is employed as a trifluoromethylating agent under a VLPC condition where the reaction and optical yields are highly appreciable. Mechanistically, the light excites the Ir complex, which oxidizes the enamine compound through a single-electron transfer mechanism; the enamine radical adds with the alkene substrate producing carboncentered radical; thus series of reaction provides the desired compound, and the

enantioselectivity (**Figure 9**).

*α-Trifluoromethylation of aldehydes [12].*

**Figure 9.**

catalyst is regenerated [12].

(bpy)3Cl2 (where bpy is 2,2<sup>0</sup>

+

ing Ru(bpy)3

**138**

applicable and highly enantioselective [11].

intersect with the single-electron oxidation of \*

regenerates the organocatalyst (**Figures 10** and **11**).

*The direct asymmetric alkylation of aldehydes.*

**Figure 11.** *Catalytic cycle—the direct asymmetric alkylation of aldehyde.*
