Rhenium-Catalyzed Epoxide Deoxygenation: Scope and Limitations

Transfer of oxygen atoms from epoxides to triphenylphosphine is efficiently catalyzed by Tp′ReO₃ [Tp′ = hydrido-tris-(3,5-dimethylpyrazolyl)borate] in benzene at 75-105 °C. The reaction tolerates a wide variety of functional groups including ketones (conjugated or non-conjugated to the new double bond), esters, nitriles, ethers, silyl ethers and phthalimides. Relative rates vary with substitution pattern and electronics; in general, monosubstituted and 2,2-disubstituted epoxides react fastest, and cis-2,3-disubstituted systems react faster than trans. Electron-withdrawing substituents promote the reaction.