(E)-4-Alkoxy-2-formylamino-3-butenoic acid esters have been prepared in two steps from 3-alkoxy-1-isocyanopropenes. The method is based on the reaction of 3-alkoxy-1-isocyano-1-lithiopropenes, which can be generated by the treatment of 3-alkoxy-1-isocyanopropenes with LDA in THF at −78 °C, with alkylchlorocarbonates, affording 4-alkoxy-2-isocyano-3-butenoates. These isocyano esters have been easily