An organocatalytic asymmetric aldol reaction of 5-alkyl-4-nitroisoxazoles to paraformaldehyde has been developed. By using a chiral dipeptide-based urea–amide–guanidinium as the phase-transfer catalyst, the transformations were promoted by sodium acetate, leading to a range of enantio-enriched isoxazole derivatives in high yields with moderate to excellent enantioselectivities. This work represents