Eosin Y: Homogeneous Photocatalytic In-Flow Reactions and Solid-Supported Catalysts for In-Batch Synthetic Transformations

Abstract

In this paper, the most recent and significant applications of Eosin Y as an organo-photocatalyst will be discussed, focusing the attention on enabling technological aspects in homogeneous photochemical flow reactions, as well as on recent developments in solid-supported catalyst applications for batch synthetic transformations.

Organocatalytic alkylation and photoorganocatalyst-free acylation of azomethine imines by Hantzsch esters under blue LED light

“…15 Repeating the reaction with the photoorganocatalyst DPZ (E 1/2 (*P/P À ) = +1.37 V) and eosin Y (E 1/2 (*P/P À ) = + 0.78 V) were found to give lower product yields of 66 and 72% yield, respectively (entries 3 and 4). 16,17 With 4CzPN as the catalyst, a screening of other solvents produced mixed results with no reaction or a lower product yield of 70% obtained for experiments performed in water or 1,4-dioxane (entries 5 and 6). In contrast, the analogous reaction with acetonitrile in place of DMF as the solvent was found to result in a near quantitative product yield of 99% being obtained (entry 7).…”

“…[1][2][3][4][5][6][7][8] One of the most powerful synthetic tools to re-emerge in the last decade for the rapid assembly of molecular complexity from readily accessible substrates in a single operation is photocatalysis. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] An illustrative example of this is a study showing the reductive radical-radical coupling of difluorobromoesters and -amides with azomethine imines exploiting an Ir(I) complex as the photocatalyst under blue LED light (Scheme 1a). 4 This was followed by an approach to prepare N-(b-aminoalkyl)pyrazolidin-3-ones that relied on the Ru(II)mediated addition of N,N-dimethylanilines to azomethine imines under blue LED light (Scheme 1b).…”

Immobilized Rose Bengal as Photocatalyst for Metal‐Free Thiocyanation of Azaheterocycles under Continuous Flow Conditions

“…One possibility to solve this issue consists in anchoring the photocatalyst onto an inert support; [28] in this way, the catalytic species could be easily removed upon a completed reaction, facilitating the work‐up and, possibly, the reuse in further transformations [29,30] . Few examples of Eosin Y [31–34] and Rose Bengal [34–42] supported materials have been already reported in literature, and their use in photochemical applications confirm that the treatment and purification of the target compound have been greatly facilitated. In this context, we wish to report here our findings on the use of Rose Bengal supported onto Merrifield resin in the direct photochemical metal‐free C‐3 thiocyanation of indoles under continuous flow conditions, originally reported by Li and coworkers [20] …”

Photoredox-Catalyzed 1,4-Peroxidation–Sulfonylation of Enynones: A Three-Component Radical Coupling Approach for the Synthesis of Highly Functionalized Allenes

“…Based on the control experiments, a plausible reaction mechanism of the photoredox catalysis of Eosin Y for 1,4-peroxidation–sulfonylation of enynones is proposed in Scheme . With the maximum absorption of Eosin Y around 530 nm, the application of green LED’s generates the photoexcited state of [Eosin Y]* that subsequently undergoes a single electron transfer to TBHP to give a t -butoxy radical and a hydroxyl anion . The subsequent hydrogen abstraction by the hydroxyl anion from the sulfinic acid 2 (p K a = 7.1; TBHP p K a = 12.8) is believed to be critical since the use of sodium sulfinate 2a-Na led to the epoxidation pathway of enynones 1 .…”