Pd-Catalyzed Reaction of Sterically Hindered Hydrazones with Aryl Halides: Synthesis of Tetra-Substituted Olefins Related to <i>iso</i>-Combretastatin A4
PdCl2(MeCN)2 in combination with dppp proved to be a powerful and efficient catalyst for the coupling of stericallyhindered N-arylsulfonylhydrazones with aryl halides, thus providing a flexible and convergent access to tetrasubstituted olefins related to iso-combretastatin A4 in good yields. This new protocol has been applied successfully to the formal synthesis of biphenylisopropylidene 4-pyridine