Scheme 2. Conditions: (a) propylamine, 43 °C, 23 h, 99%; (b) 5 M HCl, 5 min, 91%; (c) methyl 4-iodobutyrate, DIPEA, MeCN, 70 °C, 6.5 h, 98%; (d) propylamine, 47 °C, 5 d, 93%; (e) TFA, 1:1 MeOH–H2O, 5 min, 98%; (f) MeI, 3:1 MeCN–H2O, 97%.
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