Palladium epoxide hydrogenolysis

Newman et al. found that the hydrogenolysis of 1,2-epoxydecane over Raney Ni in ethanol at 150°C and 6.2 MPa H2 gave an approximately 9 1 mixture of 1- 2-decalol, while the ratio was reversed to 1 10-20 when the epoxide was hydrogenated with addition of a small amount of sodium hydroxide.18 In contrast, the course of the hydrogenolysis of styrene oxide was not affected by acid or alkali 2-phenylethanol was always formed preferentially. Mitsui et al. investigated the hydrogenation of 1,2-epoxydecane in detail with nickel wire, Raney Ni, palladium wire, and Pd-C as catalysts in ethanol at 150°C and 6 MPa H2.19 The results summarized in Table 13.1... 

Palladium on barium sulfate has been used in the hydrogenolysis of epoxides in natural product synthesis. The reaction in equation (25) illustrates its high level of functional group compatibility. 

The furanone 42, although commercially available, could also be obtained in large amounts by epoxidation of 3,3-dimethyl-4-pentenoic acid with 3-chloroperoxybenzoic acid (MCPBA) in chloroform at room temperature (84%). After protection of the primary alcohol 42 as a benzyl ether, the carbonyl unit was reduced with diisobutylaluminum hydride in ether at -78 °C to afford the diastereomeric pair of lactols 43 in 97% yield and a ratio of approximately 2 1. The lactols were methylated with p-toluene sulfonic acid in methanol to provide the functionalized tetrahydrofurans in nearly quantitative yield. The benzyl group was removed by hydrogenolysis over palladium hydroxide on carbon to afford the alcohols 44 in 94% isolated yield use of other catalysts, such as palladium on carbon, gave less reproducible results. 

Borohydride-reduced palladium. Reduction of palladium chloride in methanol with sodium borohydride until evolution of a gas ceases leads to a black material, which is not particularly sensitive to air and is not pyrophoric. The material is useful for selective hydrogenations, It catalyzes rapid hydrogenation of bonds of the type C=C, N=N, and N=0, but not the type C=N and C=0. No hydrogenolysis of nitrogen or oxygen functions is observed in alcohols, amines, amides, esters, ethers, or lactones. Epoxides are opened to alcohols very slowly. 

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