Visible-light Assisted Cu(II) Reduction Employing Organic Dyes: Applications in the Triazole Synthesis

CASTRO-GODOY, WILLBER D.; ESCATENA FRANCO; HEREDIA, ADRIÁN A.; SCHMIDT LUCIANA C.; ARGÜELLO, JUAN E.

Carlos Paz

Encuentro; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2017

Over the last decades, interest in the synthesis of 1,2,3-triazoles has significantly increased.[1] Due to their particular properties, they are increasingly employed in several areas of chemistry such as new drug discovery, biochemistry, dendrimers, polymer chemistry, and materials science. Currently, the copper-catalyzed azide-alkyne cycloaddition (CuAAC) is the most commonly used method for the synthesis of 1,2,3-triazoles.[2-4] It is widely demonstrated that Cu(I) is the catalytically active species which leads to the exclusive formation of 1,4-disubstituted 1,2,3-triazole in CuAAC reactions.[5] In the present work, we describe the use of organic dyes as a Cu(II) reducing agent by photoredox reactions which promote the Cu(I) formation, and its use as a catalyst for the synthesis of triazoles. Several organic dyes and Cu(II) sources were tested during optimization reaction, as well as control reactions were performed in order to verify that dye, Cu(II) and visible ligth must be present at the same time to form the cataliticly active specie Cu(I). To study the reaction scope, benzyl, phenacyl, alkyl and aryl azides, as well as aryl, and alkyl terminal alkynes were tested under optimized conditions with good to excellent isolated yields. This simple and environment friendly methodology employs water as a renewable and non-toxic solvent; amount of catalyst precursor is much less than conventional methodologies (TON = 710). Metal and solvent can be recycled for up to three times without a considerable loss of efficiency, visible light through LED is used, which is inexpensive and safer that methodologies which employ UV irradiation to promote Cu(II) reduction and additives are not required. In addition, an efficient one-step one-pot procedure was designed and carried out, avoiding synthesis and handle of organic azides that many times could be unsafe. [1] G. C. Tron, T. Pirali, R. A. Billington, P. L. Canonico, G. Sorba and A. A. Genazzani, Med. Res. Rev., 2008, 28, 278. [2] M. Meldal and C. W. Tornøe, Chem. Rev., 2008, 108, 2952. [3] V. K. Tiwari, B. B. Mishra, K. B. Mishra, N. Mishra, A. S. Singh and X. Chen, Chem. Rev., 2016, 116, 3086. [4] E. Haldón, M. C. Nicasiob and P. J. Pérez, Org. Biomol. Chem., 2015, 13, 9528. [5] B. T. Worrell, J. A. Malik and V. V. Fokin, Science, 2013, 340, 457.