Unsupported copper nanoparticles in the 1,3-dipolar cycloaddition of terminal alkynes and azides

FRANCISCO ALONSO; YANINA MOGLIE; GABRIEL RADIVOY; MIGUEL YUS

Alicante

Workshop; 2nd Brazilian-Spanish Workshop on Organic Chemistry; 2010

Departamento de Química Orgánica e Instituto de Síntesis Orgánica, Universidad de Alicante

We describe our results on the synthesis of 1,2,3-triazoles, based on 1,3-dipolar cycloaddition reaction of organic azides and alkynes, catalyzed by copper nanoparticles.  The unsupported copper nanoparticles have been easily and rapidly generated from anhydrous copper(II) chloride, lithium metal, and a catalytic amount of DTBB as an electron carrier, in the absence of any stabilising additive or ligand. These nanoparticles have been found to catalyse the 1,3-dipolar cycloaddition of azides and terminal alkynes in the presence of triethylamine using THF as solvent at 65 ºC. All reactions tested were accomplished in short reaction times (10-120 min) and rendered the corresponding triazoles in good-to-excellent isolated yields. The copper nanoparticles in THF exhibited superior catalytic activity when compared with other commercially available copper sources. Based on different observations, reactions, and deuteration experiments, a reaction mechanism has been postulated in which copper(I) acetylides appear as the true intermediate species.