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Reagents and conditions: (a)208 sulfur powder, DMA, 140 °C, 20–48 h, 77–85%; (b) K2S, DMF, 80 °C, 20–48 h; (c) selenium powder, DMA, 140 °C, 36 h, 62%; (d) benzylamine or n-butylamine, KOt-Bu, toluene, 4 Å MS, 120 °C, 18 h, 60–64%; (e)210 sulfur powder, 10:1 DMF/H2O, 90 °C, 45 h, 9–10%; (f) TBAF, THF, rt, 1 h, 98%.
