**11. Continuous flow α-arylation of N,N-dialkylhydrazones under visible-light photoredox catalysis**

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, α,α<sup>0</sup> -diaryl-N,N-cycloalkylhydrazones were obtained in moderate yields, and it is to be noted that conventional methods for the same are found to be non-cost-effective and time-consuming in nature. In this typical methodology, hydrazine and aryl or heteroaryl cyanides were subjected to 455 nm blue light-emitting diodes with 1 mol % of Ir(ppy)3 as photocatalyst at 40°C with LiOAc (2 equiv) as base and DMSO as solvent to get the desired product [16] (**Figure 17**).

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 reactions yield the product. Ultimately, structurally complex α,α<sup>0</sup> -diaryl-N,Ncycloalkylhydrazones 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.

**Figure 17.** *α-Arylation of hydrazones.*

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

*Photophysics, Photochemical and Substitution Reactions - Recent Advances*

under CDC reaction conditions [15] (**Figure 16**).

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

**Figure 14.**

**Figure 15.** *γ-Alkylation of enals.*

**Figure 16.**

**142**

*α-Alkylation of aldehydes.*
