One-pot gram-scale synthesis of γ-hydroxybutenolides through catalyst-free annulation of α-amino acids with α-keto acids in water

•One-pot catalyst-free synthesis of γ-hydroxybutenolides.•The method uses water as solvent which is environmentally friendly.•The product structure was confirmed by single crystal X-ray diffraction analysis.•The synthetic route is straightforward and convenient for gram-scale synthesis.