13C NMR (600 MHz, DMSO‑d 6) δ 156.3, 152.7, 149.5, 148.4, 146.0, 140.2, 128.0, 124.5, 119.3, 113.6, 89.4, 84.4, 83.0, 81.6, 44.6, 27.0, 25.2.