2-Isocyanato-2-alkenoates 3 were obtained in good yields by the perrhenate-catalyzed decomposition of 2-azidoalkanoates 1 in the presence of diphosgene (2a) or phosgene (2b). Methyl 2-azidopropionate (lh) reacts to give a mixture of methyl 2-isocyanato-2-propenoate (3h) and methyl 2-chloro-2-isocyanatopropionate (4). The addition product 4 could easily be converted into 3h by elimination of HC1 with triethylamine at 0 C. With benzyl alcohol (5a) ...