Synthesis of dioxolanes and oxazolidines by silica gel catalysis

Ethylene glycol condensed with carbonyl compounds in the presence of silica gel or alumina, without solvent and under pressure, affords 1,3-dioxolanes. 2-Amino-2-methylpropanol also condensed with carbonyl compounds in the presence of silica gel or an acid-activated clay, without solvent and under pressure, produces oxazolidines. To explain these results, we propose that the glycol and the aminopropanol react with Brønsted (H⁺) and Lewis acid sites (Si and Al) located on the surface of the catalysts, leading to the products via various ionic intermediates. Graphical abstract: .