Efficient Indium-mediated Dehalogenation of Aromatics in Ionic Liquid Media

In the field of synthetic organic chemistry, the dehalogenations are common and interesting reactions. Typical procedures generally use electrochemical, photochemical, and ultrasonic techniques. Within the broad range of conditions for carrying out such reactions, the use of indium is of particular interest because it can be utilized in different solvents as organic media, water or without solvent. Besides, this metal is stable in air and its toxicity is lower compared with to that observed in other metals.^1,2 In the context of contributing to the development of new synthetic methodology in the field of indium chemistry, as a preliminary study, we propose the use of ionic liquid as alternative solvent to carry out dehalogenation reactions. Dehalogenation of aromatics compounds was investigated by a series of reactions under several conditions. Bromobenzene was used as a starting material and due to ionic liquids (IL) have well-known properties as green solvents, we tested this procedure changing the IL.^3,4 The treatment of bromobenzene with [bmim]Cl and [bmim]Br afforded the corresponding dehalogenated derivative in good to excellent yield. However, when using as an alternative others ionic liquids [bmim]PF₆, [bmim]BF₄, [bmpy]F₃CSO₃ and TBAF, reactions did not proceed. In order to ensure the validity of the results shown above for bromobenzene, we proceeded to extend this method for chlorinated and iodinated benzene. Our experimental results indicate that [bmim]Br is the most effective solvent for this reaction. To explore the scope of this dehalogenation reaction, we investigated the behavior of others haloaromatics and haloheteroaromatics systems using indium under [bmim]Br conditions. The yields of dehalogenated products were in moderate to excellent range. In conclusion, we have demonstrated that a reductive system consisting of an indium powder in ionic liquid allows a highly conversion of haloaromatics and haloheteroaromatics compounds. This work was supported by Bicentenario Project PSD-70, Interdisciplinary Project 27/2011, and Research Project 3901-026-81, Chemistry Faculty, Pontificia Universidad Católica de Chile. References 1 Alonso, F.; Beletskaya, I.; Yus, M. Chem. Rev. 2002, 102, 4009-4091. 2 Ranu, B. C.; Dutta, P.; Sarkar, A. J. Chem. Soc., Perkin Trans. I, 1999, 1139-1140. 3 Pavlinac, J.; Zupan, M.; Laali, K.; Stavber, S. Tetrahedron, 2009, 65, 5625-5662. 4 Sowmiah, S.; Srinivasadesikan, V.; Tseng, M-C.; Chu, Y-H. Molecules, 2009, 14, 3780-3813.