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Reagents and conditions: (a) HOTT, Et3N, CH3CN, rt, 3.5 h, 82%; (b) 4-nitrophenyl chloroformate, DIPEA, CH2Cl2, rt, 4 h, 87%; (c) 6 (0.9 equiv), Cs2CO3, DMF, rt, 3.5 h, 48%; (d) 6 (2.7 equiv), Cs2CO3, DMF, rt, 6 h, 68%; (e) HCl, CH2Cl2, rt, 3.5 h then Et3N; (f) TFA, CH2Cl2, 4 h, rt, >95% (g) HCl, CH2Cl2, rt, 3.5 h then Et3N; (h) TFA, CH2Cl2, 4 h, rt, >95%.
