Two ethyl 3-acetamido-4-aryl-6-methyl-2-oxo-3,4-dihydropyran-5-carboxylates（3） were synthesized with high diastereoselectivities and characterized by IR,NMR and MS.The configuration of 3a was confirmed by single-crystal X-ray diffraction,ethyl 3-acetamido-4-（4-nitrophenyl）-6-methyl-2-oxo-3,4-dihydropyran-5-carboxylate（3a）,C17H18N2O7.The crystal is of orthorhombic,space group Pbca with a = 11.7781（16）,b = 9.5979（10）,c = 32.115（3）,V = 3630.4（7）3,Z = 8,Mr = 362.33,Dc = 1.326 Mg/m^3,λ = 0.71073,μ（MoKα） = 0.104 mm^-1,F（000） = 1520,the final R = 0.0646 and wR = 0.1464 for 1788 observed reflections with I 〉 2σ（I）.The N-H and oxygen atom are involved in intermolecular hydrogen bonds which link the molecules into a one-dimensional chain and stabilize the structure.
