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Phosphonate esters were obtained in excellent yields from a 1 : 1 : 1 addition reaction between triphenyl phosphite, dialkyl acetylenedicarboxylate and NH acids (maleimide, succinimide and N-phenylacetamide). The stereochemistry was established by solution NMR and single X-ray crystallography for two of the phosphonate esters. Dynamic effects of the maleimide moiety was observed and determined by 1 H and 13 C NMR. The free energy of activation is established for the rotation of the maleimide moiety around the N-C bond in dimethyl (2S*,3R*)-2-(2,5-dioxo-2,5dihydropyrrol-1-yl)-3-(diphenoxyphosphoryl)butanedioate as 47 ± 2 kJ/mol.