A survey of sulfide ligands for allylic C-H oxidations of terminal olefins.

Perfect to a THT! Screening a diverse library of thioether ligands led to the discovery of tetrahydrothiophene (THT) as a highly reactive and selective ligand for Pd-catalyzed allylic CH oxidation reactions. This novel ligand system provides some of the highest reported yields for the formation of (E)-linear allylic acetates through allylic CH activation chemistry (BQ = 1,4-benzoquinone).

Palladium-catalyzed reactions of enol ethers: access to enals, furans, and dihydrofurans.

The palladium-catalyzed oxidation of alkyl enol ethers to enals, which employs low loadings of a palladium catalyst, is described. The mild oxidation conditions tolerate a diverse array of functional groups, while allowing the formation of di-, tri-, and tetrasubtituted olefins. The application of this methodology to intramolecular reactions of alkyl enol ethers containing pendant alcohols provides furan and 2,5-dihydrofuran products.

Oxidant-controlled stereoselectivity in the Pd-catalyzed allylic oxidation of cis-vinylsilanes.

The allylic oxidation of cis-vinylsilanes is reported. The reaction requires a low catalyst loading of Pd(OAc)(2) without the need for an external ligand. Interestingly, trans-vinylsilanes are unreactive, whereas allylic oxidations of cis-vinylsilanes proceed in good yields giving a single diastereo- and regioisomer of the branched allylic acetate trans-vinylsilane when benzoquinone is employed. The use of PhI(OAc)(2) as oxidant in place of benzoquinone provides the branched, cis-vinylsilane as the major product. Additionally, the first intramolecular allylic C-H etherifications of cis-vinylsilanes to give oxygen heterocycles are also described.

Allylic oxidations of terminal olefins using a palladium thioether catalyst.

A palladium catalyst that converts terminal olefins to linear allylic acetates at lower catalyst loadings and faster reaction times than current systems is reported. This reaction can be conducted using benzoquinone as the oxidizing agent or catalytic amounts of copper and hydroquinone under one atmosphere of oxygen. Preliminary reactivity studies of pi-allylpalladium complexes under our reaction conditions do not provide results similar to those obtained in the catalytic reaction, which may suggest an alternative reaction pathway. The palladium catalyst is ligated by an aryloxyalkyl aryl sulfide, which is identified as a new ligand for homogeneous catalysis.