(三) 1 H NMR δ 1.89(d, 3 H, J = 1.3 Hz), 2.14(d, 3 H, J = 1.3 Hz), 2.16(s, 3 H), 6.09(m, 1 H).
NMR δ 20.6, 27.6, 31.6, 124.3, 154.8, 198.4.