**10. Photoredox cross-dehydrogenative coupling (CDC) of aldehydes with xanthenes (chiral enamines with diaryl compounds)**

Aldehydes under the treatment with visible light underwent catalytic asymmetric cross-dehydrogenative coupling reactions with xanthenes and thioxanthenes, and it is interesting to note that xanthenes are important candidates in the dye stuff

**11. Continuous flow α-arylation of N,N-dialkylhydrazones under**

*Visible-Light Photocatalysis of Aldehyde and Carbonyl Functionalities, an Innovative Domain*

The α-arylation of aldehyde-derived N,N-dialkylhydrazones with electrondeficient aryl and heteroaryl cyanides gives rise to substituted products under visible-light conditions with the use of photoredox catalysts. These structural motifs hold interesting pharmacological activities, and by these novel technologies,


The mechanism describes that single-electron transfer occurs from Ir(III) to cyanoarene, then the oxidized Ir(IV) undergoes a second electron transfer mechanism with hydrazine forming a radical cation, and the Ir is ready for the catalytic cycle. LiOAc deprotonates the proton from hydrazine system; then various steps of

cycloalkylhydrazones were obtained in moderate yields by the repetition of the direct arylation protocol. A continuous flow procedure for the preparation of α-aryl-N,N-dialkylhydrazones on a multigram scale has also been established.

**12. Rapid access to pharmacophore fragments from β-cyanoaldehydes**

synthesis of a lignin natural product, namely, (�) bursehernin [17].

Realizing the importance of asymmetric synthesis of the late chemists, they are making use of photoredox and organocatalysis together, among which CdC bond forming reactions are very important in the construction of biologically active compounds in a stereoselective fashion. One of the CdC bond forming reactions which enable the alkylation of aldehydes with a reserved cyanide functional group in the new bond is useful for synthetic manipulations. The research article presented describes the generation of CdC bond by making use of α-bromocyanoalkylated compounds as reagents, and this reaction generated β-cyano alkyls in a single synthetic operation with stereoselectivity. In a typical experimental procedure, an aldehydic compound α-bromoacetonitrile, Ru(bpy)3Cl2, asymmetric organocatalyst, and an imidazolidinone catalyst reaction mixture is irradiated by a 26 W CFL light source. The results are highly appreciable with preparative yield and with excellent enantioselectivity. More interestingly, this useful methodology has also demonstrated a total

**13. Photocatalytic synthesis of piperazines from aldehydes and ketones**

properties such as anthelmintic, antiallergic, antibacterial, antihistaminic,

Piperazines are important class of compounds with important pharmacological


**visible-light photoredox catalysis**

*DOI: http://dx.doi.org/10.5772/intechopen.92372*

solvent to get the desired product [16] (**Figure 17**).

reactions yield the product. Ultimately, structurally complex α,α<sup>0</sup>

α,α<sup>0</sup>

**Figure 17.**

**143**

*α-Arylation of hydrazones.*

**Figure 14.** *α-Alkylation of aldehydes.*

and drug industries. The coupling reactions are very highly enantioselective with good reaction and optical yields, and it was found to tolerate many functional groups under the reaction conditions that are described by the authors. They report that they were successful in their initial attempt itself on the symmetric crossdehydrogenative coupling reaction between xanthene and pentanal employing Jørgensen's catalyst. With this protocol they developed the scope of enantioselective CDC of xanthenes with various aldehydes. Excellent product and optical yields were obtained with aliphatic aldehydes, while sterically hindered isobutyraldehyde gave poor yield but with excellent optical yield. Thioxanthenes too are tolerant under CDC reaction conditions [15] (**Figure 16**).

**Figure 16.** *Photoredox cross-dehydrogenative coupling of aldehydes with xanthenes.*

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