Abstract
The B-hydride elimination is a key step in many fundamental organometallic reactions that involve interconversion of alkyl and olefin ligands.' The commonly accepted, 4-electron-4center mechanism for this reaction2 is strongly supported by the observation of agostic interactions in many alkylmetal and allylmetal c~mplexes .~ With (q3-al1yl)palladium complexes? the elimination reaction is of special interest because it produces conjugated dienes under mild condition^.^^^ For example, the Pd(0)-catalyzed conversion of allylic acetates to dienes proceeds in common organic solvents at ambient temperatures. Lack of regiospecificity, however, limits the usefulness of this method in ~ynthesis.~ Here we report that in the presence of stoichiometric amounts of B,y-unsaturated organometallic reagents the reaction becomes highly regiospecific. Evidence is provided to support a 6-electron 6-center cyclic mechanism rather than the above mentioned 4-electron-4-center pathway. The reaction of linalyl acetate (l), geranyl acetate (2), and neryl acetate (3) with catalytic amounts of Pd(PPh3)4 produces acetic acid and a mixture of myrcene (4), (E?-ocimene (5), and (a-ocimene (6) in a ratio of 74:13:13 (Scheme 1).8 Product distribution is independent of substrate's structure (either 1, 2, or 3), solvent (dioxane, toluene, THF, chloroform), catalyst concentration, and reaction time.g Only a minor dependence on temperature is observed, with slightly higher proportions of
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