Carbamic acid, 5-hexynyl-, 1,1-dimethylethyl ester (9CI)

15252-45-6

24424-99-5

151978-58-4

General procedure for the synthesis of tert-butyl 5-hexyn-1-ylcarbamate from hex-5-yn-1-amine and di-tert-butyl dicarbonate: N-(5-hexynyl)phthalimide (4.66 g, 20.5 mmol) was dissolved in tetrahydrofuran (THF, 250 mL) and hydrazine hydrate (410 mmol, 19.8 mL) was added. The reaction mixture was refluxed for 3 h. White precipitate formation was observed after 1 h of reaction. Upon completion of the reaction, the mixture was cooled to 8 °C and filtered. The filtrate was concentrated by evaporation to give the crude product hex-5-yn-1-amine (8) as a yellow liquid. The crude amine was dissolved in THF (14 mL), water (14 mL) was added followed by sodium bicarbonate (NaHCO3, 2.27 g, 27.0 mmol). The solution was cooled to 0 °C and di-tert-butyl dicarbonate (Boc2O, 2 M in THF solution, 8.09 mL; 16.2 mmol) was added slowly via syringe. The reaction temperature was maintained for 15 min before removing the ice bath. After the reaction was continued at room temperature for 2 h, the reaction mixture was diluted with ethyl acetate (EtOAc). The organic layer was washed sequentially with water, saturated aqueous sodium bicarbonate solution and brine. The organic phase was dried and evaporated to give a crude oily product. The crude product was purified by silica gel column chromatography using cyclohexane/ethyl acetate (92/8) as eluent to give tert-butyl 5-hexyne-1-ylcarbamate (9) 1.831 g in 45% yield as a light yellow oil.