Benzothiazoles are synthesized from thiobenzanilides using riboflavin as a photosensitizer and potassium peroxydisulfate as a sacrificial oxidizing agent under visible light irradiation. The methodology accepts a broad range of functional groups and affords the 2-substituted benzothiazoles by transition-metal-free organic photoredox catalysis under very mild conditions.

A novel and sustainable procedure for the synthesis of 3-selenylindoles employing diorganyl diselenides and indoles or electron-rich arenes and promoted by visible light was developed.

A simple and green synthesis of 1,4-disubstituted 1,2,3-triazoles through the effective reduction of copper(II) assisted by organic dyes and promoted by visible light was developed. This reaction was performed under very mild conditions, using water as solvent, under a non-inert atmosphere, with low catalyst precursor loading, and in the absence of any additive. Copper and solvent recycling was successfully achieved at least three times without loss of efficiency. In addition, a safer one-step one-pot procedure was designed with very good yield.

One-pot synthesis of alkyl styryl selenides using KSeCN as selenium source.

The attainment of transition-metal catalysis and photoredox catalysis has represented a great challenge over the last years. Herein, we have been able to merge both catalytic processes into what we have called "the light-triggered CuAAC reaction". Particularly, the CuAAC reaction reveals opposite outcomes depending on the nature of the photocatalyst (eosin Y disodium salt and riboflavin tetraacetate) and additives (DABCO, Et 3 N, and NaN 3 ) employed. To get a better insight into the operating processes, steady-state, time-resolved emission, and laser flash photolysis experiments have been performed to determine reactivity and kinetic data. These results, in agreement with thermodynamic estimations based on reported data, support the proposed mechanisms. While for eosin Y (EY), Cu(II) was reduced by its triplet excited state; for riboflavin tetraacetate (RFTA), mainly triplet excited RFTA state photoreductions by electron donors as additives are mandatory, affording RFTA •− (from DABCO and NaN 3 ) or RFTAH • (from Et 3 N). Subsequently, these species are responsible for the reduction of Cu(II). For both photocatalysts, photogenerated Cu(I) finally renders 1,2,3-triazole as the final product. The determined kinetic rate constants allowed postulating plausible mechanisms in both cases, bringing to light the importance of kinetic studies to achieve a strong understanding of photoredox processes.

Saccharin is a versatile scaffold to build up different heterocycles with relevance in asymmetric catalysis, agricultural chemistry, medicinal chemistry, etc. Here, we report a photochemical strategy to obtain seven-member ring benzosultams in one step, using saccharin anion as staring material. The reaction can be improved in a photo-flow reactor and its scope was evaluated. Furthermore, computational study at the CASPT2//CASSCF level of theory was also performed in order to rationalize the involved mechanism.

The potential application of multistep continuous-flow systems has had a great impact on the syntheses of active pharmaceutical ingredients, natural products, and commodity chemicals. In this report, the highly efficient combination of a chemical reduction and a photochemical C sp 2 −H activation reaction for selenylation of biologically relevant electron-rich arenes was achieved by means of a continuous-flow process. First, the reduction of alkyl and aryl selenocyanates by Rongalite was achieved giving the corresponding diselenides; second, the photoactivation of the Se−Se bond resulted in the selenylation of electron-rich arenes, both steps from good to excellent yields. In all cases, the reaction time was shortened, and isolated yields were improved when compared to batch reaction conditions. Furthermore, connecting both reactions in a multistep continuous-flow sequence was possible even when reductive and photooxidative transformations were coupled.

A variety of N-(selenomethyl)alkyl-phthalimides (alkyl = -(CH2)n-; n = 2-5, 1a, b, d, e) and N-(selenobenzyl)propyl phthalimide (1c) were synthesized and their photochemistry was studied at λ = 300 nm. Steady-state photolysis and laser time-resolved spectroscopy studies confirmed that these reactions proceeded by direct or acetone-sensitized excitation followed by intramolecular electron transfer (ET) between Se atom and the phthalimide moiety. Two main pathways are possible after ET: proton transfer to the ketyl radical anion from the CH3Se(+)˙ or the -CH2Se(+)˙- moieties, yielding the corresponding biradicals. Collapse of these biradicals yields cyclization products with the respective endo or exo selenium-containing heterocycles. Competition between both proton transfer processes depends on the chain length of the alkyl spacer between the phthalimide and Se groups as well as the size of the cycle being formed.