engleski

Click mechanochemistry: quantitative synthesis of "ready to use" chiral organocatalysts by efficient two-fold thiourea coupling on vicinal diamines

Mechanochemical methods of neat grinding and liquid-assisted grinding have been applied for the synthesis of mono- and bis-thioureas using the click coupling of aromatic and aliphatic diamines with aromatic isothiocyanates. The ability to modify the reaction conditions allowed the optimization of each reaction, leading to the quantitative formation of chiral bis-thioureas with known uses as organocatalysts or anion sensors. Quantitative reaction yields, combined with the fact that mechanochemical reaction conditions avoid the use of bulk solvents, enabled solution-based purification methods (such as chromatography or recrystallization) to be completely avoided. Importantly, by using selected model reactions, we also demonstrate that the described mechanochemical reaction procedures can be readily scaled up to at least one gram amount. In that way, mechanochemical synthesis provided a facile way to fully transform valuable enantiomerically pure reagents into useful products that could be immediately applied for a designed purpose. This was demonstrated by using some of the mechanochemically prepared reagents as organocatalysts in a model Morita-Baylis-Hillman reaction and as cyanide ion sensors in organic solvents. The use of electronically and sterically hindered o-phenylenediamine revealed that mechanochemical reaction conditions could be readily optimized to form either the 1:1 or the 1:2 click coupling product, demonstrating that reaction stoichiometry can be more efficiently controlled than in solution synthesis. In this way it was demonstrated that excellent stoichiometry control by mechanochemistry, previously esta- blished for mechanochemical syntheses of cocrystals and coordination polymers, can also be achieved in the context of covalent bond formation.

mechanochemistry

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