摘要
An innovative method was developed for the performance of aldol additions in an irreversible fashion by the use of calcium metal impregnated silica gel (Ca@SiO2) as a remarkable reducing reagent. In this approach, Ca@SiO2 drove the reaction forward, prevented reversibility, and ensured the formation of the desired products. Thus, in the presence of Ca@SiO2 (3.0 equiv), aldehydes (1.0 equiv) condensed with ketones (1.0 equiv) in 2-MeTHF to yield α,β-unsaturated enones in 71–90% yields at 25 °C. Additionally, a domino reaction involving successive aldol addition, dehydration, and Michael addition was developed for the preparation of 1,5-diketones. Accordingly, when aldehydes (1.0 equiv) were allowed to react with ketones (2.2 equiv) and Ca@SiO2(4.0 equiv), 1,5-diketones were produced in 67–88% yields. These reactions involved radical processes, where Ca@SiO2 abstracted two α hydrogen atoms from ketones and the oxygen atom from aldehydes to form CaH2@SiO2 and CaO@SiO2, respectively. These species were confirmed by powder X-ray diffraction analysis. The resultant impregnated silica gel species were solid and insoluble in the reaction mixtures, which made the addition reactions irreversible. This method represents a significant advancement in aldol condensation reactions and offers the advantages of both atom economy and atom efficiency.