Self-assembled, hollow molecular structures are appealing as synthetic hosts for mediating chemical reactions. However, product binding has inhibited catalytic turnover in such systems, and selectivity has rarely approached the levels observed in more structurally elaborate natural enzymes. We found that an aqueous organopalladium cage induces highly unusual regioselectivity in the Diels-Alder coupling of anthracene and phthalimide guests, promoting reaction at a terminal rather than central anthracene ring. Moreover, a similar bowl-shaped host attains efficient catalytic turnover in coupling the same substrates (although with the conventional regiochemistry), most likely because the product geometry inhibits the aromatic stacking interactions that attract the planar reagents to the host.

Furfural and 5-hydroxymethylfurfural (HMF) are important platform chemicals in biorefinery. Reduction of furfural or HMF with H 2 over heterogeneous catalysts is the simplest way to convert the oxygen-rich compounds. However, the process can involve many types of reactions such as hydrogenation of the CO bond, hydrogenation of the furan ring, C−O hydrogenolysis, rearrangement, C−C dissociation, and polymerization. Hydrogenation reactions are most studied in line with hydrogenations of other α,βunsaturated aldehydes, and it becomes possible to produce each product selectively: furfuryl alcohol, tetrahydrofurfuryl alcohol, 2,5-bis(hydroxymethyl)furan, or 2,5-bis(hydroxymethyl)tetrahydrofuran. Total reduction of side substituents to give 2-methylfuran or 2,5-dimethylfuran is another well-known reaction. Rearrangement and C−O hydrogenolysis reactions have been recently investigated, and they can give useful products such as cyclopentanone, 1,5-pentanediol, and 1,6hexanediol. Ongoing studies of the reaction mechanisms are also reviewed.

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The ceria-supported rhenium catalyst modified with palladium (ReO x –Pd/CeO2 (Re = 2 wt %, Pd/Re = 0.25)) is still the best catalyst for simultaneous hydrodeoxygenation. Higher Re loading amount decreased the activity. The simultaneous hydrodeoxygenation of cyclic vicinal diols occurs with high cis-stereoselectivity. ReO x –Pd/CeO2 catalysts were characterized by means of XRD, TEM, H2-TPR, XAFS, XPS, Raman, and DFT calculations. The Re species on ReO x –Pd/CeO2 (Re = 2 wt %, Pd/Re = 0.25) catalyst after reduction and after stoichiometric reaction of 1,2-hexanediol to 1-hexene were ReIV and ReVI, and the ReIV species were converted to ReVI through the stoichiometric reaction. The Re species on ReO x –Pd/CeO2 are proposed to be randomly located on the CeO2 surface, and probably only monomeric Re species have catalytic activity for simultaneous hydrodeoxygenation. This model can explain the higher activity of Re = 2 wt % catalyst than those of higher Re loading catalysts. The reaction is proposed to proceed by the tetra/hexavalent redox cycle of the Re center in the catalysis followed by hydrogenation.