Scheme 4.
(a) MW, 100–150 °C, 10–20 min; (b) Na2S2O4, NH3·H2O, THF or 1,4-dioxane/H2O (1:1), r.t. 3 h; (c) HCOOH/Pd-C, Et3N/CH3CN, reflux, 1–3 h.
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