Facile one-pot palladium-catalyzed sequential coupling to diarylmethanes by using aryl methyl ketones as the methylene donors

Article abstract of DOI:10.1002/ejoc.201300594

A novel palladium-catalyzed coupling reaction of an aryl methyl ketone with two molecules of an aryl halide to yield symmetric diarylmethanes is described. In the facile one-pot reaction, the aryl methyl ketone acts as a formal methylene donor. The experimental facts, including TLC monitoring, speculated intermediates as the raw materials, analysis of the cesium benzoate coproduct by ex situ IR spectroscopy, and the cross-coupling reactions of two different aryl halides, indicate a mechanism involving a palladium-catalyzed sequential two-step coupling process, in which the presence of a trace amount of H ₂O is indispensable. The reaction is applicable to a broad spectrum of substrates and delivers the products in good to excellent yields. Access to unsymmetrical diarylmethanes with this method is also explored and various factors are discussed. An aryl methyl ketone is used as the methylene donor to couple with two molecules of an aryl halide for the synthesis of various symmetric diarylmethanes under palladium catalysis. The mechanism involves a two-step coupling process in which the presence of a trace amount of H ₂O is indispensable. The cross-coupling to unsymmetrical diarylmethanes with this method is also explored. Copyright