A 31.07 g (82.75 mmol) portion of ethyl (E)-3-[1-benzyloxy-3-(tert-butoxycarbonylamino)cyclobutan-3-yl]acrylate was dissolved in 300 ml of nitromethane to which, while cooling in an ice bath with stirring, was subsequently added dropwise 13.37 ml (82.75 mmol) of diazabicycloundecene. After 10 minutes of stirring, the ice bath was detached and the reaction mixture was stirred at room temperature for 1 hour. While cooling in an ice bath with stirring, the reaction solution was acidified by gradually adding 10% citric acid aqueous solution and then mixed with ethyl acetate to effect separation of layers. The resulting organic layer was washed with saturated sodium bicarbonate aqueous solution and then with saturated brine. The aqueous layer was extracted with ethyl acetate, and the organic layer was dried over anhydrous sodium sulfate. After filtration, the solvent was evaporated under a reduced pressure to give 35.12 g (97.2%) of the title compound. This compound was used in the following reaction without purification.
