## 2 Eosin Y as Organocatalyst in Photochemical Flow Reactions
### Continuous Flow Photocatalytic Perfluoroalkylation Mediated by Eosin Y  
In 2014, [PERSON] and [PERSON] developed an important example of a continuous flow two-step procedure for the synthesis of \(\alpha\)-CF\({}_{3}\)-substituted carbonyl compounds under photoredox catalysis [26]. In their study, Eosin Y was proved the best catalyst in terms of conversion and selectivity for the \(\alpha\)-trifluoromethylylation of ketones compared to the Ru(bpy)\({}_{3}\)Cl\({}_{2}\) catalyst employed a few years earlier by [PERSON] to promote the same chemical transformation [27]. Initially, the desired ketones were converted into the corresponding silylenol ethers using trimethylsilyl trilate (TMSOTf) and diisopropylhylamine (iPr\({}_{2}\)NEt) under fluidic conditions. The silylenol ether so generated was then fed into a second fluidic device and subjected to visible light in order to promote the radical trifluoromethylation using Eosin Y as a photoredox catalyst and triflyl chloride (CF\({}_{3}\)SO\({}_{2}\)Cl) as a source of CF\({}_{3}\) radicals (Scheme 5). The formation of the desired silylenol ether was achieved in transparent fluorinated ethylene propylene (FEP) tubing (1/8\({}^{\circ}\) in diameter) at room temperature (RT) in only 2 min using tetrahydrofuran (THF) as a solvent. Eosin Y was introduced together with the substrate in order to avoid early interaction with the trifluoromethylation reagent. The silylenol ether was not isolated and was directly combined with triflyl chloride into a second flow reactor coiled around a glass cylinder in which a commercial cool-white household compact fluorescent lamp was inserted. This two-step process required 20 min only for completion and led to the formation of the corresponding trifluoromethylated ketones with high yields (56-87%), using low amounts of Eosin Y (0.5 mol%). In the same year, [PERSON] and co-workers reported the photocatalytic perfluoroalkylation of pyrroles and indoles using different perfluoroalkanes in the presence of Eosin Y as a photoredox catalyst [28]. The microreactor was obtained with transparent perfluoroalkoxy (PFA) capillary tubing (500 \(\mu\)L in volume; internal diameter, 750 \(\mu\)m), and the mixture was irradiated with white LEDs for 30 min as the residence time (Scheme 6). A solution of Eosin Y (5 mol%) and \(N\),\(N\),\(N\),\(N^{\prime}\)-tetramethyl-1,2-ethanediamine (TMEDA) was combined with a solution of the heteroarene premixed with the desired perfluoroalkyl iodides under continuous flow conditions. The presence of TMEDA is necessary to close the catalytic cycle, and the desired products were obtained with yields ranging from 30% to 99%. Lower yields  
Figure 5: Continuous-flow visible light-induced preparation of \(\alpha\)-trifluoromethyl ketones catalyzed by Eosin Y. FEP = fluorinated ethylene propylene. were observed when using perfluoroalkyl bromides, since it is known that they are less effective in promoting this type of transformation. The same group, after a slight modification of the continuous flow setup, was able to perform the trifluoromethylation of the heteroarenes using dangerous gaseous CF3I. In this case, a mass flow controller was introduced in the system, and \(N\)-methylpirrole and 2-methylindole were functionalized with 75% and 47% yields, respectively. More recently, [PERSON] and co-workers reported a technological improvement of this transformation obtained by a systematic study on LED emission bands (350-700 nm) with identical irradiance [29]. A homemade two-dimensional continuous-flow platform (0.85 mL total volume) equipped with an LED array (12 high-power LEDs, 1.6 W each) was used to perform the addition of nonafluoro-1-iodobutane (8) to 2-methylindole (9) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and Eosin Y (2 mol%) as a photocatalyst. Under these conditions, the catalyst loading and the reaction time were significantly reduced compared to in [PERSON]'s work, and the desired product (10) was obtained with 70% yield and 90% selectivity after 4.2 min.