Synthesis of Ortho/Ortho′-Substituted 1,1-Diarylethylenes through Cross-Coupling Reactions of Sterically Encumbered Hydrazones and Aryl Halides

The reactivity of sterically hindered N-tosylhydrazones 2 featuring ortho/ortho'-substituents on the aromatic ring with various ortho-, meta-, and para-substituted aryl halides 3 was investigated. To accomplish successfully this challenging coupling, fine-tuning of the reaction conditions were required. The newly established PdCl2(MeCN)(2)/Xphos/NaO-t-Bu/F-benzene system in a sealed tube is compatible with a broad spectrum of both coupling partners, regardless of their electronic and steric nature. This protocol has been applied successfully to the synthesis of a xanthene derivative.