Scheme 11.
a) 210 °C, 5 h, 76%. b) Polyphosphoric acid, 150 °C, 5 h, 73. c) HNO3, 75 °C, 12 min, 93%. d) POCl3, TBBAB, MeCN, 40 °C, 30 min, reflux, 22 min, 60%. e) Py, reflux, 2 h, 63%. (f) NaOH, H2O, MeOH, reflux, 40 min, 64%.
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