13C NMR (150 MHz, DMSO‑d 6) δ 156.1, 156.0, 152.5, 152.5, 149.3, 148.9, 140.1, 139.5, 138.0, 137.7, 129.2, 128.7, 119.3, 119.3, 87.7, 86.2, 85.9, 82.1, 81.4, 72.2, 71.3, 69.9, 68.3, 61.1, 50.8, 47.7.