Gluconic acid aqueous solution: a task-specific bio-based solvent for ring-opening reactions of dihydropyrans

Gluconic acid aqueous solution (GAAS) that is a largely available bio-based chemical was proved to be an effective task-specific medium for ring-opening reactions of dihydropyrans. In the presence of nucleophiles, such as indoles, 1,3-cyclohexanediones, N,N-dimethylaniline, N-methylaniline, 2-naphthol, and resorcin, a series of 2-substituted 1, 3-dicarbonyl compounds were synthesized in good to excellent yields. The first example of ring-opening of oxa-Pictet-Spengler product with nucleophiles was also described. These results not only demonstrate the feasibility of using GAAS as a sustainable solvent, but also offer an effective way for the ring-opening reactions of dihydropyrans with nucleophiles. Because these reactions proceeded with excellent atom-economy in a sustainable bio-based solvent, the present method was thus characterized by many properties of green chemistry, such as green solvent, atom-economy, and utilization of bio-based chemicals.