Facile preparation of tert-butyl 1-tert-butoxycarbonylaminocyclopent-3-enecarboxylate from inexpensive starting materials

1,5-C,C-Cycloalkylation of tert-butyl acetoacetate (1) with cis-1,4-dichloro-2-butene (2) followed by the haloform reaction of the product in NaOH solution and subsequent Curtius degradation in tert-butyl alcohol furnished tert-butyl 1-tert-butoxycarbonylaminocyclopent-3-enecarboxylate (5) in 32% overall yield.