Scheme 1.
Reaction conditions: (i) t-BuOH, 110 °C, 6 h, 90%; (ii) CoCl2·6H2O, NaBH4, MeOH, 0 °C to rt, 2 h, 83%; (iii) Et3N, DMF, 60 °C, 14 h, 57% (6a) and 16% (6b); (iv) secondary cyclic amines, K2CO3, DMF, 120 °C, 14 h, 79–92%.
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