3.1.1. Synthesis of (E)-3-(dimethylamino)-1-(2-hydroxy-4,5-dimethoxyphenyl)prop-2-en-1-one (2)

The previously reported literature procedures were used, but starting with 2-hydroxy-4,5-dimethoxyacetophenone (**1**) [34,44]. <sup>1</sup>H NMR (400 MHz, DMSO) δ 14.76 (s, 1H), 7.83 (d, *J* = 12.0 Hz, 1H), 7.31 (s, 1H), 6.41 (s, 1H), 5.85 (d, *J* = 12.0 Hz, 1H), 3.78 (s, 3H), 3.75 (s, 3H), 3.17 (s, 3H), 2.99 (s, 3H). <sup>13</sup>C NMR (100 MHz, DMSO) δ 189.35, 159.65, 154.95, 154.74, 141.13, 111.98, 111.41, 100.78, 89.38, 56.95, 55.71, 44.96, 37.54.

3.3.3. Synthesis of 3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-6,7-dimethoxy-4H-chromen-4-one (5)

The previously reported literature procedures were used but starting with the 3-iodo flavone compound (**3**) [34,45]. For the complete assignment for the proton atoms and carbon atoms, additional two-dimensional NMR such as HMBC (heteronuclear multiple bond correlation), HMQC (heteronuclear multiple-quantum correlation) and TOCSY (total correlation spectroscopy) were performed. <sup>1</sup>H NMR (400 MHz, DMSO-*d6*) δ 8.34 (s, 1H, H-2), 7.47 (s, 1H, H-5), 7.16 (s, 1H, H-8), 7.15 (d, 1H, H-2′, *J* = 2.1 Hz), 7.06 (dd, 1H, H-6′, *J* = 8.4, 2.1 Hz), 6.88 (d, 1H, H-5′, *J* = 8.4 Hz), 4.27 (s, 4H, 3′, 4′-CH2), 3.93 (s, 3H, 7-OCH3), 3.88 (s, 3H, 6-OCH3); 13C NMR (400 MHz, DMSO-*d6*) δ 173.9 (C-4), 154.2

: 341.0980; Found: 341.1032.

**Scheme 1.** Synthetic procedures for the title compound **5**. **Scheme 1.** Synthetic procedures for the title compound **5**.

#### *3.2. Crystal Structure of Isoflavone Compound 5* 3.1.2. Synthesis of 3-iodo-6,7-dimethoxy-4H-chromen-4-one (3)

OCH3), 55.7 (6-OCH3). HR/MS (m/z): Calcd. for (M+H)<sup>+</sup>

The asymmetric unit of compound **5** consists of two independent molecules **5I** (C1–C19) and **5II**  (C20–C38). In each independent molecules, two methylene groups C18–C19 (**5I**) and C37–C38 (**5II**) in corresponding 1, 4-dioxane rings are disordered over two positions with relative occupancies of 0.599(10) (**5I**) and 0.812(9) (**5II**) for the major component **A**, and 0.401(10) (**5I**) and 0.188(9) (**5II**) for the minor component **B**, respectively (Figure 1A). From a macroscopic point of view, two independent molecules **5I** and **5II** are roughly superimposed over each other as shown in Figure 1B. The slightly modified literature procedures were used, but starting with previously obtained enamine **2** [34,44]. After the completion of the reaction, the precipitate was formed. The resulting solid was filtered and was washed with cold methanol. The solid compound of iodoflavone (**3**) was pure and used for the next reaction without further purifications. <sup>1</sup>H NMR (400 MHz, DMSO) δ 8.73 (s, 1H), 7.37 (s, 1H), 7.31 (s, 1H), 3.90 (s, 3H), 3.85 (s, 3H). <sup>13</sup>C NMR (101 MHz, DMSO) δ 171.82, 158.31, 154.69, 152.04, 147.91, 114.46, 104.22, 100.44, 86.58, 56.62, 56.00.
