Synthesis of Tetrahydrofurans via Chemoselective Addition of organolithium and Grignard Reagents to γ-Chloroketones in Deep Eutectic Solvents and Water

Among saturated oxygen heterocycles, substituted tetrahydrofuran derivatives are important structural components of several natural compounds.1 Synthesis and functionalization of 2,2- disubstituted tetrahydrofurans, in particular are generally based on Williamson’s intramolecular cyclization of γ-chloroalcohols as a result of reaction with different organometallic compounds. Volatile organic solvents generally used in laboratories or in industrial processes may cause environmental problems, because their accumulation in the atmosphere, thereby contributing to ozone depletion and smog in urban areas. Thus, to further assess the potential impact of more ecofriendly solvents in organolithium chemistry, we turned our attention to the so-called Deep Eutectic Solvents (DESs)2, which were introduced by Abbott and co-workers in 2003.3 DESs are formed by mixing a hydrogen-bond donor (e.g., urea) and a hydrogen-bond acceptor (e.g., the quaternary ammonium salt choline chloride), two solid starting materials with higher melting points than the eutectic mixture. Very recent independent contribution from Hevia4 and our group5 have shown that the reactions of simple or functionalized organolithiums can be nicely performed in DESs at room temperature and under air competitively with protonolysis. In this communication, the formation of 2,2-disubstituted tetrahydrofuran derivated through the direct addition of organolithium and Grignard reagents to 4- cholobutyrophenone, chosen as model substrate, in both DESs and water. Different eutectic mixture and different organometallic’s concentrations influence on the yields of the final products. The influence of different eutectic mixtures and of the concentration of the employed organometallic species on the yield of the final products will be tackled as well. References: 1. (a) Wolfe, J. P.; Hay, M. B. Tetrahedron 2007, 63, 261; (b) Lorente, A.; Lamariano-Merketegi, J.; Albericio, F.; Alvarez, M. Chem. Rev. 2013, 113, 4567; 2. Francisco, M.; van den Bruinhorst, A.; Kroon, M. C. Angew. Chem. Int. Ed. 2013, 52, 3074; 3. A. P. Abbott, G. Copper, D. L. Davies, R. K. Rasheed, V. Tambyrajah Chem. Commun. 2003, 70; 4. Hevia, Angew. Chem, Int. Ed., 2014, 53, 5969-5973; 5. Mallardo, V.; Rizzi, R.; Sassone, F.; Mansueto, R.; Perna, F. M.; Salomone, A.; Capriati. V., Chem Comm. 2014, 50, 8655.