Palladium-catalyzed nucleophilic substitution of benzylic esters

We found that benzylic carbonates or acetates undergo nucleophilic substitution in the pres- ence of a palladium complex. The palladium catalyst, which is prepared in situ from [Pd(η³-C₃H ₅)(cod)]BF₄ and bidentate bisphosphine DPPF, is effective for the reaction of benzyl carbonate with malonate carbanion, giving the desired benzylmalonate in high yield. Choice of the ligand is crucial for the palladium catalysis. Amines, phenols, and sulfinates work as nucleo- philes for the palladium-catalyzed benzylic substitution. The activation of the benzylic carbon-oxygen bond with the palladium complex is applied to the cross-coupling of benzyl esters with organometallic compounds or the [4 + 2] cycloaddition of o-(silylmethyl)benzyl carbonates with alkenes. The latter reaction is equivalent to the Diels-Alder reaction of ortho-qui- nodimethanes with dienophiles.