Allylic Substitution in CEJ


Congrats to our collaborators in @ SU, the Samec group. The latest paper on green allylic substitutions is out in Chem. Eur. J.

Tsuji-Trost Reaction of Non-Derivatized Allylic Alcohols
Sunisa Akkarasamiyo,​ Supaporn Sawadjoon,​ Andreas Orthaber,* Joseph Samec* 
just accepted

Palladium-catalyzed allylic substitution of non-derivatized enantioenriched allylic alcohols with a variety of uncharged N-, S-, C- and O-centered nucleophiles using a bidentate BiPhePhos ligand is described. A remarkable effect of the counter ion (X) of the XPd[kappa-2-BiPhePhos][eta-3-C3H5] was observed. When ClPd[kappa-2-BiPhePhos][eta-3-C3H5] (complex I) was used as catalyst, non-reproducible results were obtained. Study of the complex by X-ray crystallography, 31P NMR spectroscopy, and ESI-MS showed that a decomposition occurred where one of the phosphite ligands was oxidized to the corresponding phosphate generating ClPd[kappa-1-BiPhePhosphite-phosphate][eta3-C3H5] species (complex II). When the chloride was exchanged to the weaker coordinating OTf- counter ion the more stable Pd[kappa-2-BiPhePhos][eta-3-C3H5]+ + [OTf] - (complex III) was formed. Complex III performed better and gave higher enantiospecificities in the substitution reactions. Complex III was evaluated in Tsuji-Trost reactions of stereogenic non-derivatized allylic alcohols. The desired products were obtained in good to excellent yields (71-98%) and enantiospecificities (73-99%) for both inter- and intramolecular substitution reactions. The methodology was applied to key steps in total synthesis of (S)-Cuspareine and (+)-Lentiginosine. A reaction mechanism involving a palladium hydride as a key intermediate in the activation of the hydroxyl group is proposed in the overall transformation.

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