Phosphine oxide allylic bromides

Scheme 16 Cu-catalysed AAA phosphonate and phosphine oxide allylic bromides...

One of the most important transformations catalysed by palladium is the Heck reaction. Oxidative addition of palladium(O) into an unsaturated halide (or tri-flate), followed by reaction with an alkene, leads to overall substitution of a vinylic (or allylic) hydrogen atom with the unsaturated group. For example, formation of cinnamic acid derivatives from aromatic halides and acrylic acid or acrylate esters is possible (1.209). Unsaturated iodides react faster than the corresponding bromides and do not require a phosphine ligand. With an aryl bromide, the ligand tri-o-tolylphosphine is effective (1.210). The addition of a metal halide or tetra-alkylammonium halide can promote the Heck reaction. Acceleration of the coupling can also be achieved in the presence of silver(I) or thallium(I) salts, or by using electron-rich phosphines such as tri-tert-butylphosphine. ... 

Aryl iodides are more reactive towards oxidative addition than aryl bromides, and a selective Heck coupling (without phosphine ligands) with an unsaturated side chain left the bromide in place. A second Heck reaction of this bromide with an allylic alcohol was used to introduce a second side chain. Cyclization of the amide on to the allylic alcohol was achieved with palladium catalysis, not as might have been expected with palladium(O) but instead with palladium(ll), to produce the seven-membered ring. Finally, the conjugated double bond was reduced and the sulfonamide removed under photolytic conditions. 

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