Calcium-Impregnated Silica Gel as a Reducing Agent in Domino Reactions for Bond Formations.

The reagent Ca@SiO2 was obtained by impregnation of silica gel with calcium metal. The presence of Ca@SiO2 allowed aldehydes to condense with ketones in 2-MeTHF, which resulted in α,β-unsaturated cyclohexenones in 73-90% yields through a radical domino process. Furthermore, Ca@SiO2 was used to induce a Darzens reaction for the efficient production of α-keto trans-epoxides from benzaldehydes and α-bromo ketones. Being a free-flowing powder, Ca@SiO2 was easy to handle and facilitated chemoselectivity among many functional groups.