Crystal facet-dependent upgrading of saccharides over barium peroxide to synthesize C-glycoside ketones†

Transformation of abundant and easily accessible carbohydrates to high-value chemicals is of the essence in the field of biorefinery. However, selective conversion of unprotected saccharides faces great challenges regarding the peculiarity of multi-functional groups. Herein, barium peroxide (BaO₂) with a preferential crystal facet presented excellent performance in the direct Knoevenagel condensation of various saccharides with acetylacetone for the synthesis of C-glycoside ketones. Characterization methods including XRD, TG-DSC, Raman spectroscopy, SEM, and TEM revealed that commercial barium oxide (BaO) calcinated under an air atmosphere could react with oxygen to generate the new species of BaO₂. Moreover, the relative proportion of each crystal facet of BaO₂ could be controlled by regulating the calcination conditions. Also, BaO₂ with the (110) facet exhibited better reactivity than that with the dominant (002) crystal facet. Combining the results from experimental studies and DFT calculations, it was revealed that the different adsorption energies of the substrates on diverse crystal facets could modulate the reaction path and the construction of C–C bonds could proceed efficiently on the BaO₂ (110) facet. In this study, we developed a convenient and practical procedure to prepare BaO₂ with preferential crystal facets, which could be used as a novel solid base catalyst for the sustainable upgrading of carbohydrate platforms.