Example 17: Methyl 4-(N-carbamoylimino)benzoate (2.18 g, 9.18 mmol) and triethylamine (1.02 mL, 7.32 mmol) were dissolved in anhydrous methanol (100 mL), followed by addition of di-tert-butyl dicarbonate (3.0 g, 13.8 mmol). The reaction mixture was heated at 40 °C for 5 h under nitrogen protection. After completion of the reaction, the mixture was cooled and concentrated under reduced pressure. The resulting residue was diluted with ethyl acetate (100 mL) and subsequently washed with aqueous sodium bicarbonate. The aqueous layer was then extracted with dichloromethane (2 x 30 mL). The organic phases were combined, dried and concentrated. Purification by fast column chromatography (silica gel, 80 g, eluent: 0-30% ethyl acetate/hexane) afforded methyl 4-(N-(tert-butoxycarbonyl)formamidinyl)benzoate as a white solid (1.98 g, 77% yield).The NMR (500 MHz, CDCl3) data were as follows: δ 8.09 (d, 2H), 7.91 (d, 2H), 3.94 (s 3H), 1.55 (s, 9H); no amidine NH protons were observed.
