Reactions of polyfluoroarylzinc compounds with Vilsmeier-Haack reagent; new synthesis of polyfluorinated aromatic aldehydes and acetales

Polyfluoroarylmetallic compounds are the important group of polyfluoroarenes. Among the chemical transformations of polyfluoroarylmetallic compounds, it is of interest to study the properties of polyfluoroaromatic zinc compounds and their role as reactive intermediates. Polyfluoroaromatic zinc compounds were prepared from chloropentafluorobenzene and perfluoroarenes [1,2]. Recently, these organozinc compounds were converted to hydro-, bromoperfluoroarenes, perfluorobiaryls, allylpolyfluoroarenes, N,N-dimethyl-bis(polyfluoroaryl)methanamines, polyfluoroaromatic ketones [1-4]. Search for the ways of synthesis of polyfluoroaromatic aldehydes is another important aspect of chemistry of polyfluoroarylzinc compounds. We have found that interaction of these organozinc compounds with Vilsmeier-Haack reagent formed from oxalyl chloride and DMF, and subsequent treatment of the reaction mixtures with water led to the corresponding polyfluoroaromatic aldehydes. When methanol was used instead of water, polyfluorinated acetales were obtained. From 1,4-dibromo-2,3,5,6-tetrafluorobenzene and zinc in the presence of tin (II) chloride in DMF, dizinc compound was obtained that was then converted to 2,3,5,6-tetrafluoroterephthalaldehyde by reaction with Vilsmeier-Haack reagent. The mechanisms of transformations are discussed. References [1] A.O. Miller, V.I. Krasnov, D. Peters, V.E. Platonov and R. Miethchen, Tetrahedron Lett., 2000, 41, 3817-3819. [2] A.S. Vinogradov, V.I. Krasnov and V.E. Platonov, Russ. J. Org. Chem., 2008, 44, 95-102. [3] A.S. Vinogradov, V.I. Krasnov and V.E. Platonov, Coll. Czech. Chem. Commun. 2008, 73, 1623–1630. [4] A.S. Vinogradov, V.I. Krasnov and V.E. Platonov, Russ. J. Org. Chem., 2010, 46, 344-351.