Pd-catalyzed reaction of sterically hindered hydrazones with aryl halides: synthesis of tetra-substituted olefins related to iso-combretastatin A4.

PdCl(2)(MeCN)(2) in combination with dppp proved to be a powerful and efficient catalyst for the coupling of sterically hindered 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 CYP17 inhibitor, 12b, of biological interest.