In this work, we developed the catalytic guanylation of thiourea using Ru(bpy) 3 Cl 2 as a photocatalyst under irradiation by visible light. The conversion of various thioureas to the corresponding guanidines was achieved using 1−5 mol % of photocatalyst in a mixture of water and ethanol at room temperature. Key benefits of this reaction include the use of photoredox catalyst, low-toxicity solvents/base, ambient temperature, and an open-flask environment.The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.orglett.0c02770.General procedure, materials and methods, copies of 1 H and 13 C NMR and HRMS spectra of compounds 2a−3j, and EDX-SEM spectrum of PbSO 4 (PDF)

The conversion of waste into high-value materials is considered an important sustainability strategy in modern chemical industries. A large volume of shell waste is generated globally from mussel cultivation. In this work, mussel shell waste (Perna viridis) is transformed into individual calcium carbonate plates (ICCPs) and is applied as a support for a heterogeneous catalyst. Palladium nanoparticles (3-6 nm) are deposited with an even dispersion on the ICCP surface, as demonstrated by X-ray diffraction and scanning electron microscopy. Using this system, Sonogashira cross-coupling reactions between aryl iodides and terminal acetylenes were accomplished in high yields with the use of 1 % Pd/ICCP in the presence of potassium carbonate without the use of any copper metal or external ligand. The Pd/ICCP catalyst could also be reused up to three times and activity over 90 % was maintained with negligible Pd-metal leaching. This work demonstrates that mussel shell waste can be used as an inexpensive and effective support for metal catalysts in coupling reactions, as demonstrated by the successful performance of the Pd-catalyzed, copper-free Sonogashira cross-coupling process.

Metal-free synthesis of guanidine from thiourea under visible light irradiation in water was successfully developed. Using 1-5% mol of inexpensive and commercially available phenazine ethosulfate as a photocatalyst in the presence of 1% CTAB as surfactant with K2CO3 as an additive base, transformations of a variety of thiourea into corresponding guanidine under visible light irradiation were achieved in moderated to high yields. The advantages of this reaction included the use of metal-free photocatalyst, water as a non-toxic solvent and ease for operating at room temperature in open-flask manner.

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