Specific allylic-allylic coupling procedures effected by ligand-induced elimination from di(allylic)palladium species

Bis(allylic)palladium complexes can be induced to undergo reductive elimination by replacement of phosphine ligands in the system with π-acidic ligands. The product 1,5-diencs, formed in high yield, are predominantly the ‘head-to-head’ coupled isomers. The bis(allylic)palladium intermediatesmay be formed by addition of an allylic Grignard or trialkyl(allylic)tin reagent to an (η³-allyl)palladiuin chloride complex, or by 1,3-diene condensation. The latter process leads to cydodimerization, ‘unusual’ for palladium catalysed reactions.