General procedure for the synthesis of tert-butyl furan-3-yl carbamate from 3-furoic acid and tert-butanol: To a solution of toluene (800 mL) containing 3-furoic acid (54.4 g, 485 mmol), triethylamine (105 mL, 753 mmol), and tert-butanol (25.2 mL, 786 mmol) was added slowly and dropwise at 45 °C at room temperature diphenylphosphoryl azide (157.8 mL, 732 mmol) at 45 °C. After dropwise addition, the reaction mixture was heated to reflux for 6 hours, followed by stirring at room temperature overnight. Upon completion of the reaction, the reaction mixture was diluted with water (1000 mL) and extracted twice with ethyl acetate (1000 mL). The organic layers were combined, washed sequentially with water (800 mL) and brine (800 mL), decolorized by activated charcoal, dried, filtered and concentrated in vacuum to give a brown semi-solid product. The semi-solid product was crystallized by a solvent mixture of dichloromethane (300 mL) and hexane (600 mL) to finally obtain tert-butyl furan-3-yl carbamate (61.5 g, 78% yield). The structure of the product was confirmed by 1H NMR (300 MHz, CDCl3): δ 7.71 (s, 1H), 7.30-7.24 (m, 1H), 6.43 (s, 1H), 6.27 (s, 1H), 1.75-1.32 (s, 9H).
