Synthesis
The general procedure for the synthesis of tert-butyl (2-bromothiophene-3-yl)carbamate from tert-butyl N-(3-thienyl)carbamate was as follows: N-bromosuccinimide (4.73 g, 26.70 mmol) was added batchwise to tert-butyl-N-(3-thienyl)carbamate (5.32 g, 26.70 mmol) to a boiling solution in dichloromethane (260 mL). After the addition was completed with vigorous stirring, the temperature of the heating bath was raised to 65 °C and maintained for 20 min, after which the reaction mixture was allowed to cool to room temperature. The reaction mixture was washed with water, dried with anhydrous magnesium sulfate, filtered and concentrated. Purification by fast column chromatography (silica gel 60, 230-400 mesh, eluent ratio 4:1 hexane:ethyl acetate) afforded a clear oily product, which was crystallized after standing (7.24 g, 97% yield).
References
[1] Patent: US9255096, 2016, B1. Location in patent: Page/Page column 46
[2] Patent: US2006/154875, 2006, A1. Location in patent: Page/Page column 7; 12
[3] Patent: US2014/121198, 2014, A1. Location in patent: Paragraph 0790; 0792
[4] Patent: WO2016/144848, 2016, A1. Location in patent: Page/Page column 40
[5] Patent: WO2016/144846, 2016, A1. Location in patent: Page/Page column 61
