¹³C NMR (176 MHz, DMSO) δ 168.19 (s, 1C), 147.35 (s, 1C), 136.21 (s, 1C), 129.14 (s, 1C), 128.56 (s, 1C), 128.27 (s, 1C), 126.48 (s, 1C), 95.93 (s, 1C), 42.53 (s, 1C).