Solvent-free copper-catalyzed click chemistry for the synthesis of N-heterocyclic hybrids based on quinoline and 1,2,3-triazole

• DOI: 10.3762/bjoc.13.232
• Publication Date: 2017-11-06T09:58:13Z
• Authors: Martina Tireli; Silvija Maračić; Stipe Lukin; Marina Juribašić ...; Dijana Žilić; Mario Cetina; Ivan Halasz; Silvana Raić-Malić; Krunoslav Užarević
• Keywords: Science; Electron spin resonance (ESR) spectroscopy; Q; Organic chemistry; electron spin resonance (ESR) spectroscopy; 01 natural sciences; Full Research Paper; 0104 chemical sciences; 3. Good health; Raman monitoring; Chemistry; QD241-441; quinolone; solid-state click chemistry; quinolone ; click chemistry ; mechanochemistry ; Raman monitoring ; Electron spin resonance (ESR) spectroscopy; 13. Climate action; quinoline; click chemistry; in situ Raman monitoring; mechanochemistry

Copper-catalyzed mechanochemical click reactions using Cu(II), Cu(I) and Cu(0) catalysts have been successfully implemented to provide novel 6-phenyl-2-(trifluoromethyl)quinolines with a phenyl-1,2,3-triazole moiety at O-4 of the quinoline core. Milling procedures proved to be significantly more efficient than the corresponding solution reactions, with up to a 15-fold gain in yield. Efficiency of both solution and milling procedures depended on the p-substituent in the azide reactant, resulting in H < Cl < Br < I reactivity bias. Solid-state catalysis using Cu(II) and Cu(I) catalysts entailed the direct involvement of the copper species in the reaction and generation of highly luminescent compounds which hindered in situ monitoring by Raman spectroscopy. However, in situ monitoring of the milling processes was enabled by using Cu(0) catalysts in the form of brass milling media which offered a direct insight into the reaction pathway of mechanochemical CuAAC reactions, indicating that the catalysis is most likely conducted on the surface of milling balls. Electron spin resonance spectroscopy was used to determine the oxidation and spin states of the respective copper catalysts in bulk products obtained by milling procedures.