Base-catalyzed heterogeneous synthesis of flavanone via a series reaction scheme involving the Claisen-Schmidt condensation between benzaldehyde and 2'-hydroxyacetophenone to form 2'-hydroxychalcone, and the subsequent isomerization of 2'-hydroxychalcone to flavanone, has been studied on pure MgO and lithium promoted MgO. Reactions were conducted at 160 ˚C and atmospheric pressure. The effect of the basic properties of the catalyst on the catalytic activity and selectivity towards flavanone was investigated by using different loadings of lithium. Lithium causes an increase in the concentration of sites of medium and high strength. The addition of lithium improved the initial reaction rates when compared to unpromoted MgO. No significant differences were however the selectivity towards flavanone between lithium promoted samples and pure MgO, suggesting that the presence of strong basic sites has an effect only on the Claisen-Schmidt step that precedes the isomerization of 2'-hydroxychalcone. ATR-FTIR spectroscopic studies were performed to investigate the adsorption and reaction between 2'-hydroxyacetophenone and benzaldehyde in the presence of dimethylsulfoxide (DMSO) on pure MgO and lithium-promoted MgO. The results were compared to gas phase studies conducted previously in our group and suggest both, similarities but also differences under the two sets of conditions.