M.C. White/Q Chen, Chem 153 兀- Allyl chemistry351 Week of December 2. 2002 Anti attack of allenes on(T-allylpalladium complexes Pd(dba 2 mol% CH3CN or Toluene Pdl PdLn E=CO,Me Pd(dba To support the proposed mechanism involving the intermediate (aT-allyl)palladium complex shown above, the authors no reaction demonstrate that the corresponding trans-allylic pivalate does f-BucOr CH3CN or not react under identical reaction conditions Toluene The authors speculate that the electron-withdrawing nature of the dba ligand increases the electrophilicity of the allyl group of the(a-allyl)palladium intermediate, and thus renders the allyl group susceptible to nucleophilic attack by the electron-rich double bond of the allene. Pd(dba trans attack HVE of allene (dba)Pd trans t-BucOr HLE E=COMe Pd(dba)z cis olefin β hydride elimination Cl Cl The pathway via trans attack on the allene is blocked upon the addition of LiCl. The authors rationalize this result by invoking the formation of a Pd-ate complex in which the dba ligand has been replaced with chloride anions. This intermediate(a-allyllpalladium complex lacking electron-withdrawing ligands alternatively undergoes olefin insertion followed by B-hydride elimination to give the corresponding cis-fused bicycle Tietze ACIEE 35: 101124-1125M.C. White/Q. Chen, Chem 153 π-Allyl chemistry -351- Week of December 2, 2002 Anti attack of allenes on (π-allyl)palladium complexes Tietze ACIEE 1997 35:10 1124-1125. t-BuCO2 · E E Pd(dba)2 2 mol% CH3CN or Toluene · PdLn PdLn E E E E E = CO2Me E H E H 76 % yield t-BuCO2 · E E E = CO2Me Pd(dba)2 2 mol% CH3CN or Toluene no reaction The authors speculate that the electron-withdrawing nature of the dba ligand increases the electrophilicity of the allyl group of the (π-allyl)palladium intermediate, and thus renders the allyl group susceptible to nucleophilic attack by the electron-rich double bond of the allene. To support the proposed mechanism involving the intermediate (π-allyl)palladium complex shown above, the authors demonstrate that the corresponding trans-allylic pivalate does not react under identical reaction conditions · E E t-BuCO2 E = CO2Me Pd(dba)2 1 eq. Pd(dba)2 1 eq. LiCl 4 eq. · E E · E E (dba)Pd Pd Cl Cl E H E H E H E H (dba)Pd trans attack of allene E E H E H E cis olefin insertion H H Pd Cl Cl 88% 90% β-hydride elimination trans cis The pathway via trans attack on the allene is blocked upon the addition of LiCl. The authors rationalize this result by invoking the formation of a Pd-ate complex in which the dba ligand has been replaced with chloride anions. This intermediate (π-allyl)palladium complex lacking electron-withdrawing ligands alternatively undergoes olefin insertion followed by β-hydride elimination to give the corresponding cis-fused bicycle