To a solution of freshly prepared (S)-2-(4-amino-2-bromo-6-methylphenyl)-2-tert-butoxyethyl pivalate (7 g, 18.1 mmol) in HOAc (90 mL) was added KSCN (1.76 g, 18.1 mmol) at r.t. The reaction mixture was stirred at r.t. for 0.5 h. Pyridinium perbromide (5.79 g, 18.1 mmol) was added slowly over a period of 10 min, and stirred at r.t for 2 h. The mixture was alkalized to pH=8 using saturated aqueous NaHCO3 solution, then extracted with EtOAc (3×600 mL). The combined organic layers were dried over anhydrous Na2SO4, filtered, concentrated in vacuo, and purified by silica gel column (Petroleum Ether:EtOAc (10:1→5:1)) to afford (S)-2-(2-amino-7-bromo-5-methylbenzo[d]thiazol-6-yl)-2-tert-butoxyethyl pivalate (2.74 g, 34.3%) as yellow solid. LCMS-ESI+: calc'd for C19H27BrN2O3S: 443.1 and 445.1 (M+H+); found: 443.1 and 445.1 (M+H+). 1H-NMR: 400 MHz, (CD3OD) δ: 7.15 (s, 1H), 5.53-5.49 (m, 1H), 4.31-4.26 (m, 1H), 4.17-4.13 (m, 1H), 2.64 (s, 3H), 1.15 (s, 9H), 1.11 (s, 9H).
