4.1 General information

Unless otherwise noted, all reactions were conducted in oven-dried round-bottom flasks under an argon atmosphere. Solvents were dried and freshly distilled from Na (THF and 1,4-dioxane) under an argon atmosphere. All reagents were from commercial sources without further purification unless otherwise noted. The silica gel (200–300 mesh, Qingdao Marine Chemical Inc., Qingdao, China) was used for column chromatography. Thin layer chromatography (TLC) was carried out on GF plates (0.25 mm layer thickness, Qingdao Marine Chemical Inc.) and was visualized by ultraviolet light (254 nm, if applicable) and phosphomolybdic acid (50 g/L) in EtOH following heating as developing agents. Unless otherwise noted, yields reported were for isolated spectroscopically pure compounds.

1H, 13C, and 19F NMR spectra were recorded on ADVANCE III AM-400 MHz, ADVANCE III AM-500 MHz and ADVANCE III 600 MHz spectrometers (Bruker) at ambient temperature. The residue solvent protons (1H) or the solvent carbons (13C) were used as internal standards. 1H NMR data are presented as chemical shifts in parts per million downfield from tetramethylsilane [multiplicity, coupling constant (hertz), integration]. Chemical shifts (δ) are given in parts per million with reference to solvent signals [1H NMR: CDCl3 (7.26); 13C NMR: CDCl3 (77.16)]. The following abbreviations are used in reporting NMR data: s, singlet; brs, broad singlet; d, doublet; t, triplet; q, quartet; dd, doublet of doublets; ddd, doublet of doublet of doublets; dt, doublet of triplets; td, triplet of doublets; m, multiplet.

4.2 General procedure for preparation of 1,3-diarylpropenes 8a–8x

According to the literatures [24, 25], 1,3-diarylpropenes 8a–8 × were synthesized through Wittig reaction from commercially available benzaldehydes and the corresponding phosphonium salts. To a suspension of phosphonium salts (1.1 equiv) in THF (0.3 M) was added dropwise LiHMDS (1 M in THF, 1.1 equiv) at 0 °C, and the resulting mixture was stirred at 0 °C until a clear red solution formed (∼ 30 min); the reaction mixture was then placed in a − 78 °C cold bath. To this solution was added a THF (0.35 M) solution of benzaldehydes (1.0 equiv) over 5 min, and the resulting mixture was warmed to room temperature and stirred for 12 h. After consumption of the starting materials, the reaction was quenched by adding water at 0 °C, and the mixture was extracted with ethyl acetate. The organic layer was dried over Na2SO4 and evaporated under vacuum to give the crude product that was purified by flash column chromatography on silica gel (petroleum ether/dichloromethane, 1:0–2:1, v/v) to afford 8a–8x (for details about the structures, overall yields, and Z:E ratios, see Additional file 1: Scheme S1).

5-(3-(4-methoxyphenyl)allyl)benzo[d][1,3]dioxole (8a, 1:5 Z:E). yellow wax (477.0 mg, 87% yield); E isomer: 1H NMR (400 MHz, CDCl3) δ 7.31 (d, J = 8.7 Hz, 2H), 6.85 (d, J = 8.7 Hz, 2H), 6.77 (d, J = 7.9 Hz, 1H), 6.75 (d, J = 1.2 Hz, 1H), 6.71 (d, J = 7.8 Hz, 1H), 6.40 (d, J = 15.7 Hz, 1H), 6.19 (dt, J = 15.7, 6.9 Hz, 1H), 5.93 (s, 2H), 3.81 (s, 3H), 3.45 (d, J = 6.8 Hz, 2H).; HRMS (ESI): m/z [M – H]– calcd for C17H15O3– 267.1027; found: 267.1025.

1-bromo-2-(3-phenylprop-1-en-1-yl)benzene (8b, 3:1 Z:E). colorless oil (51.3 mg, 75% yield); Z isomer: 1H NMR (600 MHz, CDCl3) δ 7.60 (dd, J = 8.0, 0.8 Hz, 1H), 7.31 (dd, J = 4.0, 2.4 Hz, 2H), 7.29 (s, 1H), 7.28 (d, J = 3.5 Hz, 1H), 7.21 (d, J = 6.5 Hz, 2H), 7.19 (s, 1H), 7.12 (td, J = 7.8, 1.6 Hz, 1H), 6.61 (d, J = 11.3 Hz, 1H), 5.96 (dt, J = 11.3, 7.6 Hz, 1H), 3.52 (d, J = 7.5 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H12Br– 271.0128; found: 271.0125.

1-bromo-2-(3-(p-tolyl)prop-1-en-1-yl)benzene (8c, 5:4 Z:E). colorless oil (85.5 mg, 78% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.60 (d, J = 7.8 Hz, 1H), 7.32 (d, J = 7.4 Hz, 1H), 7.24 (overlapped, 1H), 7.12 (s, 1H), 7.10 (d, J = 3.6 Hz, 3H), 7.08 (d, J = 3.9 Hz, 1H), 6.60 (d, J = 11.2 Hz, 1H), 5.95 (dt, J = 11.3, 7.7 Hz, 1H), 3.48 (d, J = 7.5 Hz, 2H), 2.32 (s, 3H); HRMS (ESI): m/z [M – H]– calcd for C16H14Br– 285.0284; found: 285.0283.

1-bromo-2-(3-(4-chlorophenyl)prop-1-en-1-yl)benzene (8d, 5:2 Z:E). colorless oil (93.5 mg, 79% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.60 (d, J = 8.0 Hz, 1H), 7.27 (s, 1H), 7.25 (d, J = 3.0 Hz, 2H), 7.18 (d, J = 8.4 Hz, 1H), 7.14 (d, J = 4.9 Hz, 1H), 7.12 (s, 1H), 7.10 (s, 1H), 6.62 (d, J = 11.3 Hz, 1H), 5.91 (dt, J = 11.3, 7.6 Hz, 1H), 3.47 (d, J = 7.6 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H11ClBr– 304.9738; found: 304.9736.

1-bromo-2-(3-(4-bromophenyl)prop-1-en-1-yl)benzene (8e, 5:2 Z:E). colorless oil (86.4 mg, 72% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.61 (d, J = 7.9 Hz, 1H), 7.41 (d, J = 8.4 Hz, 2H), 7.28 (s, 1H), 7.27 (s, 1H), 7.15 (d, J = 4.0 Hz, 1H), 7.07 (d, J = 8.4 Hz, 2H), 6.63 (d, J = 11.3 Hz, 1H), 5.91 (dt, J = 11.3, 7.6 Hz, 1H), 3.46 (d, J = 7.6 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H11Br2– 348.9233; found: 348.9231.

1-bromo-2-(3-(o-tolyl)prop-1-en-1-yl)benzene (8f, 2:1 Z:E). colorless oil (72.2 mg, 64% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.61 (d, J = 8.0 Hz, 1H), 7.32 (d, J = 7.4 Hz, 1H), 7.28 (d, J = 7.3 Hz, 1H), 7.19 (d, J = 7.5 Hz, 2H), 7.17 (d, J = 2.6 Hz, 1H), 7.14 (s, 2H), 6.63 (d, J = 11.3 Hz, 1H), 5.91 (dt, J = 11.3, 7.5 Hz, 1H), 3.49 (d, J = 7.4 Hz, 2H), 2.18 (s, 3H); HRMS (ESI): m/z [M – H]– calcd for C16H14Br– 285.0284; found: 285.0285.

5-(3-(2,5-bis(benzyloxy)-4-methoxyphenyl)allyl)benzo[d][1,3]dioxole (8g, 3:5 Z:E). yellow wax (75 mg, 65% yield); E isomer: 1H NMR (500 MHz, CDCl3) δ 7.43 (s, 2H), 7.42 (s, 1H), 7.40 (s, 1H), 7.38 (d, J = 2.0 Hz, 1H), 7.36 (t, J = 1.7 Hz, 1H), 7.34 (s, 2H), 7.31 (s, 1H), 7.30 (s, 1H), 7.03 (s, 1H), 6.74 (d, J = 4.4 Hz, 1H), 6.72 (dd, J = 4.1, 2.6 Hz, 2H), 6.70–6.66 (m, 1H), 6.54 (s, 1H), 6.10 (dt, J = 15.8, 6.9 Hz, 1H), 5.93 (s, 2H), 5.07 (s, 2H), 5.04 (s, 2H), 3.83 (s, 3H), 3.43 (d, J = 6.8 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C31H27O5– 479.1864; found: 479.1861.

1-bromo-3,4,5-trimethoxy-2-(3-phenylprop-1-en-1-yl)benzene (8h, 3:2 Z:E). colorless oil (314.6 mg, 70% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.31 (s, 1H), 7.29 (d, J = 1.7 Hz, 1H), 7.28 (s, 1H), 7.27 (s, 1H), 7.19 (s, 1H), 6.95 (s, 1H), 6.27 (dt, J = 11.0, 1.7 Hz, 1H), 5.97 (dt, J = 11.0, 7.2 Hz, 1H), 3.88 (s, 3H), 3.86 (s, 3H), 3.78 (s, 3H), 3.32 (dd, J = 7.2, 1.2 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C18H18O3Br– 361.0445; found: 361.0444.

(((2-methoxy-5-(4-phenylbut-1-en-1-yl)-1,4-phenylene)bis(oxy))bis(methylene)) dibenzene (8i, 2:3 Z:E). yellow wax (47.7 mg, 65% yield); E isomer: 1H NMR (500 MHz, CDCl3) δ 7.46 (s, 1H), 7.41 (s, 2H), 7.37 (s, 3H), 7.35 (s, 1H), 7.28 (s, 2H), 7.27 (s, 1H), 7.25 (s, 1H), 7.21 (d, J = 7.1 Hz, 3H), 7.14 (d, J = 7.1 Hz, 1H), 7.01 (s, 1H), 6.69 (d, J = 16.0 Hz, 1H), 6.53 (s, 1H), 6.04 (dt, J = 15.9, 6.9 Hz, 1H), 5.09 (s, 2H), 5.02 (s, 2H), 3.82 (s, 3H), 2.78–2.73 (m, 2H), 2.51 (dd, J = 14.6, 6.8 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C31H29O3– 449.2122; found: 449.2125.

1-bromo-3,4,5-trimethoxy-2-(4-phenylbut-1-en-1-yl)benzene (8j, 1:1 Z:E). colorless oil (80.3 mg, 55% yield); Z/E mixture (1:1): 1H NMR (500 MHz, CDCl3) δ 7.29 (t, J = 7.4 Hz, 2H), 7.25 (overlapped, 4H), 7.19 (d, J = 7.2 Hz, 1H), 7.16 (d, J = 7.0 Hz, 3H), 6.90 (d, J = 7.4 Hz, 2H), 6.39–6.36 (overlapped, 2H), 6.17 (dt, J = 11.1, 1.5 Hz, 1H), 5.84 (dt, J = 11.1, 7.2 Hz, 1H), 3.86 (s, 3H), 3.85 (overlapped, 6H), 3.84 (s, 3H), 3.72 (s, 3H), 3.71 (s, 3H), 2.87 – 2.79 (m, 2H), 2.75–2.67 (m, 2H), 2.62–2.53 (m, 2H), 2.32–2.25 (m, 2H). HRMS (ESI): m/z [M – H]– calcd for C19H20O3Br– 375.0601; found: 375.0603.

4,4'-(prop-1-ene-1,3-diyl)bis(methoxybenzene) (8k, 3:5 Z:E). white wax (66.6 mg, 69% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.47–7.44 (m, 1H), 7.30 (t, J = 2.9 Hz, 2H), 7.16 (dd, J = 5.0, 2.9 Hz, 2H), 6.91 (dd, J = 5.6, 3.2 Hz, 1H), 6.88 (d, J = 2.1 Hz, 1H), 6.83 (d, J = 2.1 Hz, 1H), 6.50 (d, J = 11.5 Hz, 1H), 5.75 (dt, J = 11.5, 7.5 Hz, 1H), 3.82 (s, 3H), 3.80 (s, 3H), 3.62 (dd, J = 7.5, 1.5 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C17H17O2– 253.1234; found: 253.1231.

1-methyl-2-(3-phenylallyl)benzene (8l, 2:1 Z:E). colorless oil (64 mg, 60% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.35 (s, 1H), 7.34 (s, 2H), 7.33 (s, 2H), 7.20 (d, J = 1.9 Hz, 1H), 7.17 (d, J = 2.7 Hz, 1H), 7.16 (d, J = 2.9 Hz, 1H), 7.15 (s, 1H), 6.60 (d, J = 11.5 Hz, 1H), 5.79 (dt, J = 11.5, 7.3 Hz, 1H), 3.64 (dd, J = 7.3, 1.5 Hz, 2H), 2.22 (s, 3H); HRMS (ESI): m/z [M – H]– calcd for C16H15– 207.1179; found: 207.1175.

1-(3-(4-methoxyphenyl)allyl)-2-methylbenzene (8m, 2:3 Z:E). colorless oil (84.9 mg, 71% yield); E isomer: 1H NMR (500 MHz, CDCl3) δ 7.28 (s, 1H), 7.27 (s, 1H), 7.17 (d, J = 4.8 Hz, 2H), 7.15 (d, J = 2.2 Hz, 1H), 7.15 (s, 1H), 6.85–6.80 (m, 2H), 6.32 (d, J = 15.8 Hz, 1H), 6.19 (dt, J = 15.8, 6.5 Hz, 1H), 3.80 (s, 3H), 3.51 (d, J = 6.5 Hz, 2H), 2.34 (s, 3H); HRMS (ESI): m/z [M – H]– calcd for C17H17O– 237.1285; found: 237.1288.

1-chloro-4-(3-phenylallyl)benzene (8n, 2:1 Z:E). colorless oil (131.3 mg, 77% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.45 (d, J = 8.6 Hz, 1H), 7.35 (d, J = 3.3 Hz, 2H), 7.34 (d, J = 1.8 Hz, 1H), 7.28–7.27 (overlapped, 2H), 7.16 (d, J = 3.1 Hz, 1H), 7.14 (s, 1H), 7.13 (d, J = 2.6 Hz, 1H), 6.61 (d, J = 11.5 Hz, 1H), 5.81 (dt, J = 11.5, 7.5 Hz, 1H), 3.46 (d, J = 5.5 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H12Cl– 227.0633; found: 227.0630.

1-chloro-4-(3-(4-methoxyphenyl)allyl)benzene (8o, 4:5 Z:E). white wax (86 mg, 28% yield); E isomer: 1H NMR (500 MHz, CDCl3) δ 7.43 (d, J = 8.6 Hz, 1H), 7.31 (d, J = 2.7 Hz, 1H), 7.29 (d, J = 1.7 Hz, 1H), 7.27 (d, J = 1.9 Hz, 1H), 7.17 (d, J = 7.9 Hz, 1H), 6.92 (d, J = 8.8 Hz, 1H), 6.88 (d, J = 8.7 Hz, 1H), 6.84 (d, J = 8.8 Hz, 1H), 6.38 (d, J = 15.7 Hz, 1H), 6.16 (dt, J = 15.7, 6.9 Hz, 1H), 3.84 (s, 3H), 3.63 (d, J = 7.4 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C16H14ClO– 257.0739; found: 257.0740.

1-(3-phenylallyl)naphthalene (8p, 2:1 Z:E). yellow oil (58.7 mg, 53% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.90 (d, J = 9.0 Hz, 1H), 7.88 (dd, J = 6.5, 2.9 Hz, 1H), 7.50 – 7.48 (m, 1H), 7.48 (s, 1H), 7.48–7.46 (m, 1H), 7.43 (d, J = 3.4 Hz, 1H), 7.42 (s, 1H), 7.39 (d, J = 1.6 Hz, 2H), 7.38 (s, 1H), 7.30 (t, J = 2.0 Hz, 1H), 7.28 (s, 1H), 6.65 (d, J = 11.5 Hz, 1H), 5.95 (dt, J = 11.5, 7.2 Hz, 1H), 4.12 (dd, J = 7.2, 1.7 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C19H15– 243.1179; found: 243.1178.

1-fluoro-2-(3-phenylallyl)benzene (8q, 3:2 Z:E). colorless oil (48.9 mg, 59% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.37 (s, 1H), 7.35 (s, 2H), 7.34 (s, 1H), 7.23 (d, J = 7.2 Hz, 2H), 7.21 (s, 1H), 7.10 (dd, J = 4.5, 3.0 Hz, 1H), 7.08 (d, J = 7.5 Hz, 1H), 6.62 (d, J = 11.5 Hz, 1H), 5.83 (dt, J = 11.5, 7.5 Hz, 1H), 3.70 (d, J = 7.4 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H12F– 211.0929; found: 211.0925.

1-bromo-2-(3-(2-fluorophenyl)prop-1-en-1-yl)benzene (8r, 5:1 Z:E). colorless oil (36.8 mg, 32% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.61 (dd, J = 8.0, 0.9 Hz, 1H), 7.33 (dd, J = 7.6, 1.7 Hz, 1H), 7.31–7.28 (m, 1H), 7.20 (s, 1H), 7.19 (s, 1H), 7.15 (dd, J = 7.6, 1.7 Hz, 1H), 7.10–7.07 (m, 1H), 7.02 (dd, J = 13.4, 4.8 Hz, 1H), 6.63 (d, J = 11.3 Hz, 1H), 5.94 (dt, J = 11.3, 7.5 Hz, 1H), 3.54 (d, J = 7.6 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H12FBr– 290.0112; found: 290.0110.

1-chloro-2-(3-phenylallyl)benzene (8s, 1:1 Z:E). colorless oil (56.6 mg, 65% yield); Z/E mixture (1:1): 1H NMR (400 MHz, CDCl3) δ 7.40–7.31 (overlapped, 6H), 7.30 (s, 2H), 7.28 (s, 2H), 7.26 (overlapped, 1H), 7.24 (s, 2H), 7.18 (overlapped, 5H), 6.63 (d, J = 11.5 Hz, 1H), 6.44 (d, J = 15.5 Hz, 1H), 6.39–6.27 (m, 1H), 5.86–5.73 (m, 1H), 3.76 (d, J = 7.3 Hz, 2H), 3.65 (d, J = 6.3 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H12Cl– 227.0633; found: 227.0631.

1-bromo-2-(3-(2-chlorophenyl)prop-1-en-1-yl)benzene (8t, 5:1 Z:E). colorless oil (49.8 mg, 54% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.64–7.58 (m, 1H), 7.35 (dd, J = 7.8, 1.2 Hz, 1H), 7.30 (d, J = 2.3 Hz, 1H), 7.24 (dd, J = 7.5, 2.0 Hz, 1H), 7.21 (dd, J = 7.2, 1.3 Hz, 1H), 7.18 (dd, J = 4.3, 1.9 Hz, 1H), 7.15 (t, J = 1.9 Hz, 1H), 7.14 (s, 1H), 6.66 (d, J = 11.3 Hz, 1H), 5.94 (dt, J = 11.3, 7.5 Hz, 1H), 3.62 (dd, J = 7.5, 1.3 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H11ClBr– 304.9738; found: 304.9739.

1-fluoro-2-(3-(4-methoxyphenyl)allyl)benzene (8u, 4:5 Z:E). colorless oil (63.5 mg, 67% yield); E isomer: 1H NMR (500 MHz, CDCl3) δ 7.29–7.26 (m, 2H), 7.20 (ddd, J = 7.3, 6.2, 1.6 Hz, 2H), 7.09 (dd, J = 7.5, 1.3 Hz, 2H), 6.84 (dd, J = 8.7, 1.8 Hz, 2H), 6.41 (d, J = 15.7 Hz, 1H), 6.20 (dtd, J = 15.7, 6.9, 1.8 Hz, 1H), 3.80 (d, J = 1.2 Hz, 3H), 3.55 (d, J = 6.8 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C16H14OF– 241.1034; found: 241.1036.

prop-1-ene-1,3-diyldibenzene (8v, 5:3 Z:E). yellow oil (77.9 mg, 80% yield); Z isomer: 1H NMR (500 MHz, CDCl3) δ 7.38 (s, 1H), 7.36 (s, 2H), 7.34 (s, 2H), 7.32 (d, J = 3.3 Hz, 2H), 7.24 (s, 2H), 7.22 (d, J = 1.7 Hz, 1H), 6.60 (d, J = 11.5 Hz, 1H), 5.87 (dt, J = 11.5, 7.5 Hz, 1H), 3.69 (d, J = 7.5 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C15H13– 193.1023; found: 193.1022.

1,2-dimethoxy-4-(3-(4-methoxyphenyl)allyl)benzene (8w, 1:2 Z:E). white wax (87.8 mg, 72% yield); E isomer: 1H NMR (500 MHz, CDCl3) δ 7.30 (d, J = 8.7 Hz, 2H), 6.84 (d, J = 8.8 Hz, 2H), 6.81 (s, 1H), 6.79 (t, J = 2.1 Hz, 1H), 6.76 (d, J = 1.7 Hz, 1H), 6.39 (d, J = 15.7 Hz, 1H), 6.20 (dt, J = 15.7, 6.8 Hz, 1H), 3.87 (s, 3H), 3.87 (s, 3H), 3.80 (s, 3H), 3.47 (d, J = 6.7 Hz, 2H); HRMS (ESI): m/z [M – H]– calcd for C18H19O3– 283.1340, found: 283.1344.

2-bromo-3-(3-(3-methoxyphenyl)prop-1-en-1-yl)pyridine (8x, 5:2 Z:E). colorless oil (76.2 mg, 66% yield); Z isomer: 1H NMR (600 MHz, CDCl3) δ 8.28 (dd, J = 4.5, 1.5 Hz, 1H), 7.59 (dd, J = 7.4, 1.3 Hz, 1H), 7.25 (dd, J = 7.5, 4.8 Hz, 1H), 7.10 (d, J = 8.5 Hz, 2H), 6.85 (d, J = 8.5 Hz, 2H), 6.55 (d, J = 11.4 Hz, 1H), 6.05 (dt, J = 11.3, 7.7 Hz, 1H), 3.79 (s, 3H), 3.44 (d, J = 7.6 Hz, 2H); HRMS (ESI): m/z [M + H]+ calcd for C15H15ONBr+ 304.0332, found: 304.0336.

4.3 General procedure for Prins cyclization of 1,3-dioxanes 7

A reaction tube charged with a solution of (CHO)n (50 wt%), TfOH (10 mol%) in freshly distilled DCM (0.1 M) were stirred for 20 min at room temperature. Then the reaction mixture was cooled to 0 ℃ for 5 min, and was added of 8 (0.1 mmol, 1.0 equiv) in the DCM (0.5 M). The reaction was stirred at 0 ℃ for 4 h. Then the reaction mixture was warmed to room temperature for 20 h. The reaction was quenched with NaHCO3 saturated aqueous solution, and was extracted with dichloromethane. The combined organic layer was dried over Na2SO4, filtered, and concentrated to give the crude product that was further purified by flash column chromatography on silica gel (petroleum ether/ethyl acetate, 25:1–2:1, v/v) to afford 7a–7v, 11a, 11a′ and 11b.

5-((trans-4-(4-methoxyphenyl)-1,3-dioxan-5-yl)methyl)benzo[d][1,3]dioxole (7a). yellow solid (25.9 mg, 79% yield): mp 112.4−113.0 °C; 1H NMR (400 MHz, CDCl3) δ 7.35 (d, J = 8.5 Hz, 2H), 6.93 (d, J = 8.4 Hz, 2H), 6.66 (d, J = 7.8 Hz, 1H), 6.44 (s, 1H), 6.41 (d, J = 8.0 Hz, 1H), 5.89 (s, 2H), 5.15 (d, J = 6.2 Hz, 1H), 4.80 (d, J = 6.3 Hz, 1H), 4.21 (d, J = 9.9 Hz, 1H), 3.99 (dd, J = 11.4, 4.3 Hz, 1H), 3.83 (s, 3H), 3.43 (t, J = 11.1 Hz, 1H), 2.38 (dd, J = 13.8, 3.6 Hz, 1H), 2.35–2.23 (m, 1H), 2.00 (dd, J = 13.7, 10.8 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 159.8, 147.7, 146.0, 132.2, 131.5, 129.0, 129.0, 121.6, 114.1, 114.1, 109.1, 108.2, 101.0, 94.3, 84.5, 71.5, 55.4, 42.8, 34.4; HRMS (ESI): m/z [M + H]+ calcd for C19H21O5+ 329.1384, found: 329.1383.

(trans-5-(4-methoxyphenyl)-6,7-dihydro-5H-indeno[5,6-d][1,3]dioxol-6-yl)methanol (11a). yellow solid (3.0 mg, 10% yield): mp 167.1–169.1 ℃; 1H NMR (400 MHz, CDCl3) δ 7.09 (d, J = 8.6 Hz, 2H), 6.85 (d, J = 8.6 Hz, 2H), 6.72 (s, 1H), 6.34 (s, 1H), 5.89 (dd, J = 8.0, 1.0 Hz, 2H), 3.98 (d, J = 8.1 Hz, 1H), 3.83–3.76 (overlapped, 4H), 3.71 (dd, J = 10.6, 6.7 Hz, 1H), 3.08 (dd, J = 15.4, 8.0 Hz, 1H), 2.73 (dd, J = 15.4, 8.3 Hz, 1H), 2.65–2.54 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 158.5, 147.0, 146.8, 139.3, 136.7, 135.4, 129.4, 129.4, 114.1, 114.1, 105.7, 105.0, 101.0, 65.3, 55.4, 53.5, 53.2, 35.1; HRMS (ESI): m/z [M + H]+ calcd for C18H19O4+ 299.1278, found: 299.1278.

(cis-5-(4-methoxyphenyl)-6,7-dihydro-5H-indeno[5,6-d][1,3]dioxol-6-yl)methanol (11a′). The product was obtained under the conditions in Table 1, entry 3, as a yellow solid (4.2 mg, 14% yield): mp 98.5–100.1 ℃; 1H NMR (400 MHz, CDCl3) δ 7.05 (dd, J = 8.5, 4.3 Hz, 2H), 6.83 (d, J = 8.5 Hz, 2H), 6.69 (s, 1H), 6.33 (s, 1H), 5.89 (d, J = 7.3 Hz, 2H), 4.66 (s, 1H), 3.95 (t, J = 7.6 Hz, 1H), 3.79 (s, 3H), 3.70–3.52 (m, 2H), 3.03 (ddd, J = 14.9, 7.7, 2.4 Hz, 1H), 2.74–2.56 (overlapped, 2H); 13C NMR (100 MHz, CDCl3) δ 158.4, 146.9, 146.8, 139.2, 136.6, 135.7, 129.4, 129.4, 114.0, 114.0, 105.7, 105.0, 101.0, 69.9, 69.7, 55.4, 53.2, 51.1, 51.0, 35.6; HRMS (ESI): m/z [M + H]+ calcd for C18H19O4+: 299.1278; found: 299.1276.

((trans)-5,6-dimethoxy-1-(4-methoxyphenyl)-2,3-dihydro-1H-inden-2-yl)methanol (11b). yellow wax (15.7 mg, 50% yield); 1H NMR (400 MHz, CDCl3) δ 7.10 (d, J = 8.6 Hz, 2H), 6.86 (d, J = 8.7 Hz, 2H), 6.80 (s, 1H), 6.41 (s, 1H), 4.04 (d, J = 8.0 Hz, 1H), 3.88 (s, 3H), 3.83–3.78 (overlapped, 4H), 3.75–3.70 (overlapped, 4H), 3.12 (dd, J = 15.4, 8.1 Hz, 1H), 2.77 (dd, J = 15.4, 8.1 Hz, 1H), 2.64–2.49 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 158.4, 148.5, 148.4, 137.9, 136.9, 134.4, 129.4, 129.4, 114.1, 114.1, 108.2, 107.6, 65.4, 56.2, 56.2, 55.4, 53.5, 53.5, 35.1; HRMS (ESI): m/z [M + H]+ calcd for C19H23O4+ 315.1591, found: 315.1591.

trans-5-benzyl-4-(2-bromophenyl)-1,3-dioxane (7b). yellow oil (22.9 mg, 69% yield); 1H NMR (500 MHz, CDCl3) δ 7.63 (dd, J = 7.8, 1.5 Hz, 1H), 7.58 (dd, J = 8.0, 0.9 Hz, 1H), 7.41 (dd, J = 11.0, 4.1 Hz, 1H), 7.20 (td, J = 6.7, 2.8 Hz, 3H), 7.15 (t, J = 7.3 Hz, 1H), 6.97 (d, J = 7.2 Hz, 2H), 5.18 (d, J = 6.3 Hz, 1H), 4.96 (d, J = 9.9 Hz, 1H), 4.87 (d, J = 6.3 Hz, 1H), 3.98 (dd, J = 11.5, 4.2 Hz, 1H), 3.54 (t, J = 11.1 Hz, 1H), 2.48 (dd, J = 13.7, 3.4 Hz, 1H), 2.44–2.35 (m, 1H), 2.28 (dd, J = 13.7, 11.0 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 138.9, 138.4, 132.7, 129.9, 129.2, 128.7, 128.7,128.5, 128.5, 128.3, 126.4, 124.3, 94.4, 82.4, 71.4, 43.8, 34.1; HRMS (ESI): m/z [M + NH4]+ calcd for C17H21 O2NBr+ 350.0750, found: 350.0751.

trans-4-(2-bromophenyl)-5-(4-methylbenzyl)-1,3-dioxane (7c). colorless oil (17.7 mg, 51% yield); 1H NMR (500 MHz, CDCl3) δ 7.62 (dd, J = 7.8, 1.6 Hz, 1H), 7.58 (dd, J = 8.0, 1.1 Hz, 1H), 7.43–7.39 (m, 1H), 7.20 (td, J = 7.9, 1.7 Hz, 1H), 7.02 (d, J = 7.8 Hz, 2H), 6.85 (d, J = 7.9 Hz, 2H), 5.17 (d, J = 6.3 Hz, 1H), 4.94 (d, J = 9.9 Hz, 1H), 4.86 (d, J = 6.3 Hz, 1H), 3.98 (dd, J = 11.5, 4.2 Hz, 1H), 3.52 (t, J = 11.1 Hz, 1H), 2.44 (dd, J = 13.7, 3.4 Hz, 1H), 2.41–2.31 (m, 1H), 2.28 (s, 3H), 2.24 (dd, J = 13.7, 11.0 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 139.0, 135.9, 135.2, 132.8, 129.9, 129.2, 129.2, 129.2, 128.6, 128.6, 128.3, 124.4, 94.4, 82.5, 71.5, 43.8, 33.7, 21.1; HRMS (ESI): m/z [M – H]– calcd for C18H19O2ClBr– 381.0262, found: 381.0265.

trans-4-(2-bromophenyl)-5-(4-chlorobenzyl)-1,3-dioxane (7d). colorless oil (24.8 mg, 68% yield); 1H NMR (500 MHz, CDCl3) δ 7.64 – 7.57 (m, 2H), 7.42 (t, J = 7.5 Hz, 1H), 7.23 (dd, J = 7.8, 1.6 Hz, 1H), 7.21–7.17 (m, 2H), 6.91 (d, J = 8.3 Hz, 2H), 5.20 (d, J = 6.3 Hz, 1H), 4.96 (d, J = 9.7 Hz, 1H), 4.89 (d, J = 6.3 Hz, 1H), 3.98 (dd, J = 11.5, 4.1 Hz, 1H), 3.54 (t, J = 11.0 Hz, 1H), 2.46 (dd, J = 13.5, 3.4 Hz, 1H), 2.43–2.33 (m, 1H), 2.29 (dd, J = 13.4, 10.7 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 138.8, 136.9, 132.8, 132.2, 130.0, 130.0, 130.0, 129.2, 128.7, 128.7, 128.3, 124.2, 94.4, 82.36, 71.3, 43.8, 33.5; HRMS (ESI): m/z [M – H]– calcd for C17H15O2ClBr– 364.9949, found: 364.9948.

trans-5-(4-bromobenzyl)-4-(2-bromophenyl)-1,3-dioxane (7e). white solid (30 mg, 73% yield): mp 90.9–91.5 °C; 1H NMR (500 MHz, CDCl3) δ 7.58 (ddd, J = 13.2, 7.9, 1.3 Hz, 2H), 7.42 – 7.38 (m, 1H), 7.34–7.29 (m, 2H), 7.20 (td, J = 7.8, 1.7 Hz, 1H), 6.83 (d, J = 8.3 Hz, 2H), 5.17 (d, J = 6.3 Hz, 1H), 4.93 (d, J = 9.8 Hz, 1H), 4.86 (d, J = 6.3 Hz, 1H), 3.95 (dd, J = 11.5, 4.1 Hz, 1H), 3.51 (t, J = 11.0 Hz, 1H), 2.42 (dd, J = 13.5, 3.5 Hz, 1H), 2.33 (ddd, J = 13.8, 10.2, 5.0 Hz, 1H), 2.25 (dd, J = 13.5, 10.7 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 138.8, 137.4, 132.8, 131.6, 131.6, 130.4, 130.4, 130.0, 129.2, 128.3, 124.2, 120.2, 94.4, 82.4, 71.2, 43.7, 33.6; HRMS (ESI): m/z [M + Na]+ calcd for C17H15O2Br2Na+ 432.9409, found: 423.9607.

trans-4-(2-bromophenyl)-5-(2-methylbenzyl)-1,3-dioxane (7f). yellow oil (21.2 mg, 61% yield); 1H NMR (500 MHz, CDCl3) δ 7.61 (ddd, J = 20.9, 7.9, 1.4 Hz, 2H), 7.44–7.39 (m, 1H), 7.23–7.19 (m, 1H), 7.09–7.02 (m, 3H), 6.93–6.89 (m, 1H), 5.19 (d, J = 6.3 Hz, 1H), 5.01–4.96 (m, 1H), 4.89 (d, J = 6.3 Hz, 1H), 4.01 (dd, J = 11.6, 3.1 Hz, 1H), 3.63–3.55 (m, 1H), 2.44 (dd, J = 12.9, 7.1 Hz, 1H), 2.30 (overlapped, 2H), 1.96 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 139.1, 136.6, 136.0, 132.7, 130.6, 129.9, 129.6, 129.3, 128.2, 126.6, 125.9, 124.2, 94.4, 82.5, 71.6, 42.8, 31.5, 19.1; HRMS (ESI): m/z [M – H]– calcd for C18H18O2Br– 345.0496, found: 345.0494.

5-((trans-4-(2,5-bis(benzyloxy)-4-methoxyphenyl)-1,3-dioxan-5-yl)methyl)benzo [d][1,3]dioxole (7g). colorless oil (9.5 mg, 28% yield); 1H NMR (500 MHz, CDCl3) δ 7.49–7.29 (overlapped, 10H), 7.08 (s, 1H), 6.62 (d, J = 7.8 Hz, 1H), 6.56 (s, 1H), 6.32 (s, 1H), 6.30 (d, J = 7.9 Hz, 1H), 5.89 (dd, J = 4.3, 1.3 Hz, 2H), 5.18 (d, J = 12.1 Hz, 1H), 5.13 (s, 1H), 5.10 (d, J = 12.3 Hz, 1H), 5.06 (s, 2H), 4.81 (d, J = 10.0 Hz, 1H), 4.77 (d, J = 6.2 Hz, 1H), 3.91 (dd, J = 11.3, 4.2 Hz, 1H), 3.85 (s, 3H), 3.38 (t, J = 11.2 Hz, 1H), 2.29 (dd, J = 14.0, 3.8 Hz, 1H), 2.19–2.07 (m, 1H), 1.97 (dd, J = 14.0, 10.8 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 151.2, 150.5, 147.7, 146.0, 143.3, 137.5, 137.3, 132.5, 128.8, 128.8, 128.7, 128.7, 128.2, 128.0, 127.7, 127.7, 127.6, 127.6, 121.6, 120.3, 114.6, 109.2, 108.1, 100.9, 100.2, 99.7, 94.4, 72.1, 72.0, 71.6, 56.4, 43.1, 34.1; HRMS (ESI): m/z [M + H]+ calcd for C33H33O7+ 541.2221, found: 541.2221.

trans-5-benzyl-4-(6-bromo-2,3,4-trimethoxyphenyl)-1,3-dioxane (7h). yellow oil (32.1 mg, 76% yield); 1H NMR (500 MHz, CDCl3) δ 7.18 (t, J = 7.3 Hz, 2H), 7.11 (t, J = 7.3 Hz, 1H), 7.01 (d, J = 7.1 Hz, 2H), 6.89 (s, 1H), 5.19 (d, J = 6.1 Hz, 1H), 4.92 (d, J = 10.1 Hz, 1H), 4.82 (d, J = 6.2 Hz, 1H), 4.01 (dd, J = 11.3, 4.4 Hz, 1H), 3.94 (s, 3H), 3.85 (s, 3H), 3.83 (s, 3H), 3.44 (t, J = 11.1 Hz, 1H), 3.21 (s, 1H), 2.40 (dd, J = 14.0, 4.6 Hz, 1H), 2.18 (dd, J = 13.9, 9.9 Hz, 1H). 13C NMR (125 MHz, CDCl3) δ 154.4, 154.4, 154.0, 143.0, 138.9, 128.7, 128.7, 128.4, 128.4, 126.1, 124.4, 112.5, 94.6, 83.9, 72.2, 62.1, 60.9, 56.3, 39.1, 34.9; HRMS (ESI): m/z [M + H]+ calcd for C20H24O5Br+ 423.0786, found: 423.0786.

trans-4-(2,5-bis(benzyloxy)-4-methoxyphenyl)-5-phenethyl-1,3-dioxane (7i). yellow wax (34.7 mg, 68% yield); 1H NMR (500 MHz, CDCl3) δ 7.45 (d, J = 7.4 Hz, 2H), 7.39–7.27 (m, 8H), 7.20 (t, J = 7.4 Hz, 2H), 7.13 (t, J = 7.3 Hz, 1H), 6.99 (s, 1H), 6.95 (d, J = 7.3 Hz, 2H), 6.55 (s, 1H), 5.14 (d, J = 6.2 Hz, 1H), 5.11–4.98 (m, 4H), 4.82–4.75 (m, 2H), 4.23 (dd, J = 11.3, 4.4 Hz, 1H), 3.83 (s, 3H), 3.46 (t, J = 11.1 Hz, 1H), 2.45–2.35 (m, 1H), 2.21 (ddd, J = 13.9, 10.0, 6.6 Hz, 1H), 2.04–1.94 (m, 1H), 1.41–1.31 (m, 1H), 1.25–1.14 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 151.2, 150.4, 143.3, 141.9, 137.5, 137.3, 128.7, 128.7, 128.6, 128.6, 128.4, 128.4, 128.3, 128.3, 128.1, 127.9, 127.8, 127.8, 127.6, 127.6, 126.0, 120.5, 114.6, 99.7, 94.4, 75.5, 72.0, 72.0, 71.9, 56.4, 40.8, 32.8, 29.3; HRMS (ESI): m/z [M + H]+ calcd for C33H35O5+ 511.2478, found: 511.2478.

trans-4-(6-bromo-2,3,4-trimethoxyphenyl)-5-phenethyl-1,3-dioxane (7j). colorless oil (22.9 mg, 50% yield); 1H NMR (600 MHz, CDCl3) δ 7.21 (t, J = 7.5 Hz, 2H), 7.13 (t, J = 7.4 Hz, 1H), 7.03 (d, J = 7.3 Hz, 2H), 6.89 (s, 1H), 5.19 (d, J = 6.1 Hz, 1H), 4.87 (d, J = 10.2 Hz, 1H), 4.81 (d, J = 6.2 Hz, 1H), 4.28 (dd, J = 11.2, 4.5 Hz, 1H), 3.86 (s, 3H), 3.85 (s, 3H), 3.84 (s, 3H), 3.45 (t, J = 11.1 Hz, 1H), 2.94–2.83 (m, 1H), 2.49 (ddd, J = 14.1, 10.4, 5.6 Hz, 1H), 2.30 (ddd, J = 13.8, 10.2, 6.6 Hz, 1H), 1.42–1.32 (m, 1H), 1.34–1.26 (m, 1H); 13C NMR (150 MHz, CDCl3) δ 154.6, 154.5, 154.0, 142.9, 142.0, 128.5, 128.5, 128.3, 128.3, 126.0, 124.6, 111.9, 94.5, 84.5, 72.2, 61.9, 60.9, 56.3, 37.2, 32.9, 30.1; HRMS (ESI): m/z [M + H]+ calcd for C21H26O5Br+ 437.0958, found: 437.0955.

trans-5-(4-methoxybenzyl)-4-(4-methoxyphenyl)-1,3-dioxane (7k). white solid (21.7 mg, 69% yield): mp 113.6–115.6 °C; 1H NMR (500 MHz, CDCl3) δ 7.40 – 7.33 (m, 2H), 6.94 (d, J = 8.7 Hz, 2H), 6.88 (d, J = 8.6 Hz, 2H), 6.76 (d, J = 8.6 Hz, 2H), 5.16 (d, J = 6.3 Hz, 1H), 4.81 (d, J = 6.3 Hz, 1H), 4.23 (d, J = 10.0 Hz, 1H), 3.98 (dd, J = 11.5, 4.3 Hz, 1H), 3.83 (s, 3H), 3.76 (s, 3H), 3.44 (t, J = 11.2 Hz, 1H), 2.42 (dd, J = 13.9, 3.6 Hz, 1H), 2.37–2.26 (m, 1H), 2.03 (dd, J = 13.9, 10.8 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 159.9, 158.2, 131.7, 130.5, 129.7, 129.7, 129.0, 129.0, 114.2, 114.2, 114.0, 114.0, 94.3, 84.6, 71.6, 55.5, 55.4, 42.8, 33.8; HRMS (ESI): m/z [M + Na]+ calcd for C19H22O4Na+ 337.1410, found: 337.1411.

trans-5-(2-methylbenzyl)-4-phenyl-1,3-dioxane (7l). white wax (17.1 mg, 64% yield); 1H NMR (500 MHz, CDCl3) δ 7.47 (d, J = 7.0 Hz, 2H), 7.41 (t, J = 7.2 Hz, 2H), 7.39–7.34 (m, 1H), 7.09–7.03 (overlapped, 3H), 6.94–6.89 (m, 1H), 5.20 (d, J = 6.2 Hz, 1H), 4.87 (d, J = 6.2 Hz, 1H), 4.33 (d, J = 9.9 Hz, 1H), 3.99 (dd, J = 11.4, 4.4 Hz, 1H), 3.53 (t, J = 11.1 Hz, 1H), 2.46 (dd, J = 13.9, 3.2 Hz, 1H), 2.38–2.25 (m, 1H), 2.12 (dd, J = 13.8, 11.5 Hz, 1H), 1.97 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 139.4, 136.6, 136.1, 130.6, 129.7, 128.7, 128.7, 128.7, 127.8, 127.8, 126.5, 125.9, 94.3, 85.3, 71.7, 41.6, 32.0, 19.1; HRMS (ESI): m/z [M + NH4]+ calcd for C18H24O2N+ 286.1802, found: 286.1806.

trans-4-(4-methoxyphenyl)-5-(2-methylbenzyl)-1,3-dioxane (7 m). colorless oil (20.0 mg, 67% yield); 1H NMR (500 MHz, CDCl3) δ 7.38 (d, J = 8.6 Hz, 2H), 7.08–7.02 (overlapped, 3H), 6.93 (d, J = 8.6 Hz, 2H), 6.91 (d, J = 6.1 Hz, 1H), 5.17 (d, J = 6.2 Hz, 1H), 4.84 (d, J = 6.2 Hz, 1H), 4.26 (d, J = 9.9 Hz, 1H), 3.96 (dd, J = 11.5, 4.3 Hz, 1H), 3.83 (s, 3H), 3.51–3.47 (m, 1H), 2.45 (dd, J = 13.9, 3.2 Hz, 1H), 2.35–2.25 (m, 1H), 2.09 (dd, J = 13.8, 11.5 Hz, 1H), 2.00 (s, 3H).; 13C NMR (125 MHz, CDCl3) δ 159.9, 136.8, 136.1, 131.70, 130.6, 129.7, 129.0, 129.0, 126.5, 125.9, 114.1, 114.1, 94.3, 84.9, 71.8, 55.5, 41.6, 32.1, 19.3; HRMS (ESI): m/z [M + K]+ calcd for C19H22O3K+ 337.1201, found: 337.1200.

trans-5-(4-chlorobenzyl)-4-phenyl-1,3-dioxane (7n). white solid (16.1 mg, 56% yield): mp 100.7–102.0 °C; 1H NMR (500 MHz, CDCl3) δ 7.45–7.33 (overlapped, 5H), 7.18 (d, J = 8.4 Hz, 2H), 6.88 (d, J = 8.3 Hz, 2H), 5.18 (d, J = 6.3 Hz, 1H), 4.83 (d, J = 6.3 Hz, 1H), 4.28 (d, J = 9.9 Hz, 1H), 3.95 (dd, J = 11.5, 4.3 Hz, 1H), 3.45 (t, J = 11.1 Hz, 1H), 2.43 (dd, J = 13.9, 3.7 Hz, 1H), 2.34 (dt, J = 10.0, 4.0 Hz, 1H), 2.09 (dd, J = 13.9, 10.8 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 139.2, 136.9, 132.2, 130.1, 130.1, 128.8, 128.8, 128.8, 128.7, 128.7, 127.8, 127.8, 94.3, 85.0, 71.3, 42.6, 34.0; HRMS (ESI): m/z [M + K]+ calcd for C17H17O2ClK+ 327.0549, found: 327.0547.

trans-5-(4-chlorobenzyl)-4-(4-methoxyphenyl)-1,3-dioxane (7o). white solid (20.3 mg, 64% yield): mp 123.5 − 126.9 °C; 1H NMR (500 MHz, CDCl3) δ 7.34 (d, J = 8.7 Hz, 2H), 7.18 (d, J = 8.4 Hz, 2H), 6.93 (d, J = 8.7 Hz, 2H), 6.88 (d, J = 8.3 Hz, 2H), 5.15 (d, J = 6.2 Hz, 1H), 4.81 (d, J = 6.3 Hz, 1H), 4.22 (d, J = 9.9 Hz, 1H), 3.95 (dd, J = 11.4, 4.4 Hz, 1H), 3.83 (s, 3H), 3.44 (t, J = 11.1 Hz, 1H), 2.43 (dd, J = 13.9, 3.7 Hz, 1H), 2.31 (ddt, J = 10.6, 8.3, 5.2 Hz, 1H), 2.07 (dd, J = 13.9, 10.7 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 160.0, 137.0, 132.2, 131.4, 130.1, 130.1, 129.0, 129.0, 128.7, 128.7, 114.2, 114.2, 94.3, 84.5, 71.4, 55.5, 42.69, 34.1; HRMS (ESI): m/z [M – H]– calcd for C18H18O3Cl– 317.0950, found: 317.0951.

trans-5-(naphthalen-1-ylmethyl)-4-phenyl-1,3-dioxane (7p). yellow wax (4.2 mg, 14% yield); 1H NMR (400 MHz, CDCl3) δ 7.81 (d, J = 8.1 Hz, 1H), 7.69 (d, J = 8.2 Hz, 1H), 7.56 (dd, J = 8.1, 1.3 Hz, 2H), 7.52 – 7.47 (m, 2H), 7.45 (dt, J = 5.0, 1.8 Hz, 1H), 7.41 (dd, J = 8.2, 1.3 Hz, 1H), 7.32 (ddd, J = 8.9, 6.8, 1.9 Hz, 2H), 7.26 (d, J = 8.3 Hz, 1H), 7.13 (d, J = 6.9 Hz, 1H), 5.19 (d, J = 6.2 Hz, 1H), 4.88 (d, J = 6.2 Hz, 1H), 4.42 (d, J = 9.4 Hz, 1H), 3.90 (dd, J = 11.3, 3.8 Hz, 1H), 3.61–3.52 (m, 1H), 3.01 (d, J = 11.3 Hz, 1H), 2.56–2.41 (overlapped, 2H); 13C NMR (100 MHz, CDCl3) δ 139.5, 134.5, 134.1, 131.7, 128.9, 128.9, 128.8, 128.8, 128.0, 128.0, 127.4, 126.9, 126.0, 125.7, 125.2, 123.7, 94.2, 85.2, 71.9, 41.9, 31.8; HRMS (ESI): m/z [M + NH4]+ calcd for C21H24O2N+ 322.1802, found: 322.1805.

trans-5-(2-fluorobenzyl)-4-phenyl-1,3-dioxane (7q). colorless oil (23.9 mg, 88% yield); 1H NMR (500 MHz, CDCl3) δ 7.45 (d, J = 7.0 Hz, 2H), 7.40 (t, J = 7.3 Hz, 2H), 7.38–7.33 (m, 1H), 7.14 (td, J = 7.4, 1.8 Hz, 1H), 7.01–6.88 (overlapped, 3H), 5.18 (d, J = 6.2 Hz, 1H), 4.85 (d, J = 6.2 Hz, 1H), 4.32 (d, J = 9.8 Hz, 1H), 3.98 (dd, J = 11.5, 4.2 Hz, 1H), 3.53 (t, J = 11.2 Hz, 1H), 2.42 (overlapped, 2H), 2.27 (dd, J = 13.8, 11.0 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 162.1, 160.1, 139.1, 131.0, 131.0, 128.7, 128.7, 128.2, 128.2, 127.9, 125.5, 125.4, 124.1, 124.1, 115.5, 115.3, 94.3, 85.2, 71.3, 41.7, 27.5, 27.5; 19F NMR (376 MHz, CDCl3) δ -117.6; HRMS (ESI): m/z [M + NH4]+ calcd for C17H21O2NF+ 290.1551, found: 290.1551.

trans-4-(2-bromophenyl)-5-(2-fluorobenzyl)-1,3-dioxane (7r). yellow oil (25.6 mg, 73% yield); 1H NMR (500 MHz, CDCl3) δ 7.59 (ddd, J = 16.4, 7.9, 1.3 Hz, 2H), 7.40 (t, J = 7.1 Hz, 1H), 7.20 (td, J = 7.9, 1.7 Hz, 1H), 7.16–7.10 (m, 1H), 6.99–6.90 (m, 3H), 5.17 (d, J = 6.3 Hz, 1H), 4.96 (d, J = 9.3 Hz, 1H), 4.88 (d, J = 6.3 Hz, 1H), 3.98 (dd, J = 11.4, 3.1 Hz, 1H), 3.59 (dd, J = 13.8, 7.6 Hz, 1H), 2.41 (overlapped, 3H); 13C NMR (125 MHz, CDCl3) δ 162.3, 159.9, 138.6, 132.7, 131.0, 131.0 130.0, 129.3, 128.3, 128.2, 125.5, 125.4, 124.4, 124.1, 124.1, 115.5, 115.3, 94.4, 82.4, 71.2, 42.7, 27.3; 19F NMR (376 MHz, CDCl3) δ-117.7; HRMS (ESI): m/z [M + Na]+ calcd for C17H16O2FBrNa+ 373.0210, found: 373.0210.

trans-5-(2-chlorobenzyl)-4-phenyl-1,3-dioxane (7s). white solid (24.8 mg, 86% yield): mp 61.6–62.0 °C; 1H NMR (500 MHz, CDCl3) δ 7.46 (d, J = 7.0 Hz, 2H), 7.39 (t, J = 7.3 Hz, 2H), 7.36 (d, J = 7.2 Hz, 1H), 7.27 (dd, J = 5.7, 3.5 Hz, 1H), 7.11 – 7.07 (m, 2H), 6.94 (dd, J = 5.7, 3.6 Hz, 1H), 5.19 (d, J = 6.2 Hz, 1H), 4.86 (d, J = 6.2 Hz, 1H), 4.33 (d, J = 9.6 Hz, 1H), 3.96 (dd, J = 11.4, 4.0 Hz, 1H), 3.57 (t, J = 11.0 Hz, 1H), 2.56–2.46 (overlapped, 2H), 2.35 (dd, J = 14.5, 11.7 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 139.0, 136.4, 134.1, 130.9, 129.8, 128.7, 128.7, 128.7, 127.9, 127.9, 127.9, 126.8, 94.3, 85.3, 71.3, 41.4, 32.1; HRMS (ESI): m/z [M + H]+ calcd for C17H18O2Cl+ 289.0990, found: 289.0990.

trans-4-(2-bromophenyl)-5-(2-chlorobenzyl)-1,3-dioxane (7t). yellow oil (25.6 mg, 70% yield); 1H NMR (500 MHz, CDCl3) δ 7.62 (dd, J = 7.8, 1.6 Hz, 1H), 7.58 (dd, J = 8.0, 1.1 Hz, 1H), 7.40–7.36 (m, 1H), 7.27 (dd, J = 3.2, 2.3 Hz, 1H), 7.21 – 7.17 (m, 1H), 7.12–7.06 (m, 2H), 6.97–6.94 (m, 1H), 5.18 (d, J = 6.3 Hz, 1H), 4.99 (d, J = 9.3 Hz, 1H), 4.89 (d, J = 6.3 Hz, 1H), 3.97 (dd, J = 11.3, 3.1 Hz, 1H), 3.66–3.58 (m, 1H), 2.58–2.43 (overlapped, 3H); 13C NMR (125 MHz, CDCl3) δ 138.6, 136.3, 134.0, 132.6, 131.0, 130.0, 129.8, 129.5, 128.2, 128.0, 126.7, 124.3, 94.4, 82.4, 71.3, 42.2, 31.8; HRMS (ESI): m/z [M + H]+ calcd for C17H17O2ClBr+ 367.0095, found: 367.0095.

trans-5-(2-fluorobenzyl)-4-(4-methoxyphenyl)-1,3-dioxane (7u). yellow oil (19.9 mg, 66% yield); 1H NMR (500 MHz, CDCl3) δ 7.37 (d, J = 8.7 Hz, 2H), 7.17–7.11 (m, 1H), 7.00–6.96 (m, 1H), 6.96–6.91 (overlapped, 4H), 5.16 (d, J = 6.2 Hz, 1H), 4.83 (d, J = 6.2 Hz, 1H), 4.26 (d, J = 9.8 Hz, 1H), 3.97 (dd, J = 11.4, 4.2 Hz, 1H), 3.83 (s, 3H), 3.51 (t, J = 11.1 Hz, 1H), 2.40 (overlapped, 2H), 2.23 (dd, J = 14.2, 11.3 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 162.1, 160.1, 159.9, 131.4, 131.0, 131.0, 129.1, 128.2, 128.1, 125.6, 125.5, 124.1, 124.1, 115.5, 115.3, 114.2, 94.3, 84.7, 71.4, 55.4, 41.7, 27.6; 19F NMR (376 MHz, CDCl3) δ − 117.5; HRMS (ESI): m/z [M + H]+ calcd for C18H20O3F+ 303.1391; found: 303.1391.

trans-5-benzyl-4-phenyl-1,3-dioxane (7v). white wax (19.4 mg, 77% yield); 1H NMR (500 MHz, CDCl3) δ 7.49–7.44 (m, 2H), 7.42 (t, J = 7.4 Hz, 2H), 7.37 (dd, J = 11.4, 4.2 Hz, 1H), 7.22 (t, J = 7.3 Hz, 2H), 7.16 (t, J = 7.3 Hz, 1H), 6.97 (d, J = 7.2 Hz, 2H), 5.19 (d, J = 6.2 Hz, 1H), 4.84 (d, J = 6.3 Hz, 1H), 4.31 (d, J = 9.9 Hz, 1H), 3.99 (dd, J = 11.5, 4.4 Hz, 1H), 3.48 (t, J = 11.2 Hz, 1H), 2.49 (dd, J = 13.8, 3.6 Hz, 1H), 2.44–2.33 (m, 1H), 2.11 (dd, J = 13.8, 10.9 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 139.3, 138.4, 128.8, 128.8, 128.8, 128.8, 128.7, 128.5, 128.5, 127.8, 127.8, 126.4, 94.3, 85.1, 71.5, 42.6, 34.6; HRMS (ESI): m/z [M – H]– calcd for C17H17O2– 253.1234, found: 235.1235.

4.4 Procedure for preparation of 11a-1

To a solution of 11a (20 mg, 0.067 mmol) in dry DMF (0.67 mL) was added NaH (4 mg, 0.101 mmol) at 0 ℃ and stirred for 30 min. The mixture was then allowed to warm up to room temperature, followed by the addition of MeI (4 mg, 0.101 mmol). The reaction mixture was stirred for 15 h. The reaction diluted with water and extracted with ethyl acetate. The organic layer was dried over Na2SO4 and evaporated under vacuum to give the crude product that was purified by flash column chromatography on silica gel (petroleum ether/ethyl acetate, 10:2, v/v) to afford 11a-1.

trans-6-(methoxymethyl)-5-(4-methoxyphenyl)-6,7-dihydro-5H-indeno[5,6-d][1,3]dioxole (11a-1). white solid (18.5 mg, 88% yield): mp 156.7–157.5 ℃; 1H NMR (400 MHz, CDCl3) δ 7.08 (d, J = 8.6 Hz, 2H), 6.85 (d, J = 8.6 Hz, 2H), 6.71 (s, 1H), 6.34 (s, 1H), 5.89 (d, J = 7.6 Hz, 2H), 3.95 (d, J = 8.0 Hz, 1H), 3.80 (s, 3H), 3.49 (dd, J = 9.2, 5.1 Hz, 1H), 3.42 (t, J = 8.3 Hz, 1H), 3.33 (s, 3H), 3.07 (dd, J = 15.4, 7.9 Hz, 1H), 2.73 (dd, J = 15.4, 8.1 Hz, 1H), 2.68–2.55 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 158.4, 146.9, 146.7, 139.2, 136.7, 135.8, 129.4, 129.4, 114.0, 114.0, 105.7, 105.0, 101.0, 75.0, 59.0, 55.4, 53.1, 50.9, 35.6; HRMS (ESI): m/z [M + H]+ calcd for C19H21O4+ 313.1434, found: 313.1434.

4.5 Procedure for preparation of 6b, trans-6h, and cis-6h

Compound 7b or 7h (0.33 mmol, 1.0 equiv) was treated at 0 °C with glacial acetic acid added dropwise (5.0 equiv) and trifluoroacetic anhydride added dropwise (5.0 equiv). The reaction mixture was allowed to warm to room temperature and stirred for 2 h. The reaction was stopped by adding a cold saturated aqueous solution of NaHCO3 and then extracted with dichloromethane. The combined organic layer was dried over Na2SO4, filtered, and concentrated to obtain the crude product. The crude product was dissolved in a 1N solution of NaOH (MeOH/H2O = 9:1, 0.2 M) and stirred for 40 min. After consumption of the starting materials, the reaction was quenched by adding water at 0 °C, and the mixture was extracted with ethyl acetate. The reaction mixture was then purified by flash chromatography (petroleum ether/dichloromethane/ethyl acetate, 20:10:2, v/v) to yield 6b, trans-6h, and cis-6h.

trans-2-benzyl-1-(2-bromophenyl)propane-1,3-diol (6b). light yellow oil (99.2 mg, quantitative yield); 1H NMR (400 MHz, CDCl3) δ 7.65 (dd, J = 7.8, 1.1 Hz, 1H), 7.51 (d, J = 8.0 Hz, 1H), 7.37 (t, J = 7.5 Hz, 1H), 7.31–7.17 (overlapped, 5H), 7.14 (td, J = 7.8, 1.4 Hz, 1H), 5.17 (t, J = 4.1 Hz, 1H), 3.71 (d, J = 11.1 Hz, 1H), 3.53 (d, J = 11.0 Hz, 1H), 3.48 (d, J = 5.1 Hz, 1H), 2.93 (qd, J = 13.6, 7.8 Hz, 2H), 2.50 (s, 1H), 2.24–2.15 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 142.5, 140.1, 133.0, 129.4, 129.4, 129.1, 128.5, 128.5 128.1, 127.7, 126.3, 122.2, 76.8, 62.3, 45.9, 35.2; HRMS (ESI): m/z [M + Cl]– calcd for C16H17O2ClBr– 335.0106, found: 335.0104.

trans-2-benzyl-1-(6-bromo-2,3,4-trimethoxyphenyl)propane-1,3-diol (trans-6h). yellow oil (51 mg, 52% yield); 1H NMR (400 MHz, CDCl3) δ 7.20 (t, J = 7.4 Hz, 2H), 7.13 (t, J = 7.3 Hz, 1H), 7.02 (d, J = 7.2 Hz, 2H), 6.87 (s, 1H), 5.16 (t, J = 8.6 Hz, 1H), 4.01 (s, 3H), 3.89 (overlapped, 1H), 3.85 (s, 3H), 3.82 (s, 3H), 3.76 (d, J = 9.9 Hz, 1H), 3.71 (dd, J = 11.1, 5.6 Hz, 1H), 2.92 (s, 1H), 2.55–2.36 (overlapped, 3H); 13C NMR (100 MHz, CDCl3) δ 153.7, 153.0, 141.9, 140.3, 129.0, 129.0, 128.4, 128.4, 126.9, 126.1, 117.8, 112.1, 78.0, 64.8, 61.9, 60.9, 56.3, 48.5, 34.4; HRMS (ESI): m/z [M + Na]+ calcd for C19H23 O5BrNa+ 433.0621, found: 433.0625.

cis-2-benzyl-1-(6-bromo-2,3,4-trimethoxyphenyl)propane-1,3-diol (cis-6h). yellow oil (32.5 mg, 33% yield); 1H NMR (400 MHz, CDCl3) δ 7.32–7.22 (overlapped, 4H), 7.19 (t, J = 6.9 Hz, 1H), 6.88 (s, 1H), 5.12 (t, J = 8.8 Hz, 1H), 4.02 (s, 3H), 3.85 (s, 3H), 3.83 (overlapped, 4H), 3.43 (s, 2H), 3.10 (dd, J = 13.4, 3.2 Hz, 1H), 2.92–2.78 (m, 1H), 2.34–2.23 (m, 1H), 1.89 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 153.4, 152.8, 141.8, 140.7, 129.5, 129.5, 128.5, 128.5, 126.6, 126.0, 116.5, 112.4, 76.1, 62.2, 62.0, 60.9, 56.3, 48.8, 32.8; HRMS (ESI): m/z [M + Na]+ calcd for C19H23O5BrNa+ 433.0621, found: 433.0623.

4.6 Procedure for preparation of 12a and 12b through UM reaction

A Schlenk tube was equipped with a magnetic stirring bar, and loaded with Cs2CO3 (200 mol %), CuI (20 mol %), ethane-1,2-diamine (22 mol %), 6b (1.0 equiv) and 1,4-dioxane (0.1 M) under air. The tube was sealed, evacuated, and refilled with argon. The reaction mixture was stirred at 120 °C for 12 h. Afterward, The mixture was filtered and the solid was washed with ethyl acetate, and the filtrates were concentrated under reduced pressure. The residue was purified by silica gel chromatography (petroleum ether/dichloromethane/ethyl acetate, 60:10:2—10:10:2 v/v) to give the product 12a and 12b.

trans-3-benzylchroman-4-ol (12a). white solid (4.8 mg, 21% yield, 34% brsm): mp 125.6 − 128.2 °C; 1H NMR (400 MHz, CDCl3) δ 7.36–7.31 (overlapped, 2H), 7.26 (overlapped, 3H), 7.24–7.18 (overlapped, 2H), 6.89 (t, J = 7.4 Hz, 1H), 6.85 (d, J = 8.6 Hz, 1H), 4.52 (d, J = 2.9 Hz, 1H), 4.11 (d, J = 2.8 Hz, 1H), 4.09 (s, 1H), 2.89 (dd, J = 13.6, 8.4 Hz, 1H), 2.73–2.62 (m, 1H), 2.39–2.27 (m, 1H), 1.68 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 154.5, 139.3, 130.3, 130.1, 129.3, 129.3, 128.7, 128.7, 126.5, 124.3, 120.7, 117.1, 65.1, 65.1, 40.1, 33.0; HRMS (ESI): m/z [M – H]– calcd for C16H15O2– 239.1078; found: 239.1075.

trans-2-benzyl-1-phenylpropane-1,3-diol (12b). white solid (3.9 mg, 17% yield, 20% brsm): mp 66.3 − 69.8 °C; 1H NMR (400 MHz, CDCl3) δ 7.37 (s, 2H), 7.36 (s, 2H), 7.32–7.27 (m, 1H), 7.25 (d, J = 7.5 Hz, 2H), 7.18 (t, J = 7.3 Hz, 1H), 7.13 (d, J = 7.4 Hz, 2H), 4.76 (d, J = 6.1 Hz, 1H), 3.75 (dd, J = 11.0, 2.1 Hz, 1H), 3.56 (dd, J = 11.0, 5.5 Hz, 1H), 3.18 (s, 1H), 2.71 (overlapped, 2H), 2.59 (dd, J = 13.8, 9.5 Hz, 1H), 2.10 (ddd, J = 8.9, 5.9, 2.9 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 143.5, 140.2, 129.2, 129.2, 128.6, 128.6, 128.5, 128.5, 127.8, 126.4, 126.4, 126.2, 78.1, 63.3, 48.5, 34.9; HRMS (ESI): m/z [M + Cl]– calcd for C16H18O2Cl– 277.1001, found: 277.1001.

4.7 Procedure for preparation of 14a, 14b and 15

A solution of 12a (1.0 equiv) in 17% HCl–MeOH (1:1, 0.05 M) was heated at 90 °C for 1 h. After being cooled to room temperature, the reaction mixture was concentrated under reduced pressure to give the crude residue, diluted with dichloromethane and water, and the layers were separated. The water layer was extracted with dichloromethane. The combined organic layers were dried over Na2SO4 and concentrated in vacuo to give the residue which was purified by silica gel column chromatography (petroleum ether/dichloromethane, 8:1–0:1,v/v) to give 14a, 14b and 15.

cis-3-benzyl-4-methoxychromane (14a). yellow oil (2.1 mg, 16.5% yield); 1H NMR (400 MHz, CDCl3) δ 7.33 (overlapped, 2H), 7.22 (overlapped, 4H), 7.13–7.09 (m, 1H), 6.85 (d, J = 7.7 Hz, 2H), 4.20 (t, J = 10.7 Hz, 1H), 4.09 (ddd, J = 10.6, 3.9, 0.7 Hz, 1H), 3.92 (d, J = 2.9 Hz, 1H), 3.38 (s, 3H), 2.86 (dd, J = 13.5, 8.4 Hz, 1H), 2.66 (dd, J = 13.5, 7.2 Hz, 1H), 2.35 (tdd, J = 11.1, 7.1, 3.7 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 154.6, 139.6, 130.7, 130.0, 129.3, 129.3, 128.6, 128.6, 126.3, 121.2, 119.4, 117.0, 73.7, 65.8, 56.1, 39.3, 32.9; HRMS (ESI): m/z [M – H]– calcd for C17H17O2– 253.1234; found: 253.1236.

trans-3-benzyl-4-methoxychromane (14b). yellow oil (2.3 mg, 18% yield); 1H NMR (400 MHz, CDCl3) δ 7.34–7.27 (overlapped, 2H), 7.26 (overlapped, 1H), 7.25–7.20 (overlapped, 2H), 7.17 (d, J = 7.6 Hz, 2H), 6.94 (d, J = 7.4 Hz, 1H), 6.90 (d, J = 8.5 Hz, 1H), 4.26 (dd, J = 10.9, 2.2 Hz, 1H), 4.01 (d, J = 10.8 Hz, 1H), 3.96 (s, 1H), 3.36 (s, 3H), 2.58 (d, J = 2.5 Hz, 1H), 2.56 (s, 1H), 2.38–2.28 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 154.6, 139.5, 131.8, 129.2, 128.6, 129.2, 128.6, 126.4, 120.3, 119.9, 117.1, 75.9, 64.5, 55.8, 38.1, 34.7; HRMS (ESI): m/z [M – H]– calcd for C17H17O2– 253.1234; found: 253.1232.

3-benzyl-2H-chromene (15). colorless oil (2.4 mg, 21.6% yield); 1H NMR (400 MHz, CDCl3) δ 7.32 (t, J = 7.3 Hz, 2H), 7.24 (overlapped, 3H), 7.06 (td, J = 7.8, 1.6 Hz, 1H), 6.93 (dd, J = 7.4, 1.5 Hz, 1H), 6.84 (t, J = 7.4 Hz, 1H), 6.75 (d, J = 8.0 Hz, 1H), 6.16 (s, 1H), 4.65 (s, 2H), 3.43 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 153.0, 137.6, 134.1, 129.1, 129.1,128.7, 128.7, 128.6, 126.8, 126.3, 121.4, 120.5, 115.5, 68.2, 40.0; HRMS (ESI): m/z [M + Br]– calcd for C16H14OBr– 301.0234; found: 301.0235.

4.8 Procedure for preparation of trans-12h, cis-12h, trans-12c and cis-12c

Trans-12h, cis-12h, trans-12c and cis-12c were prepared using the same protocol as the preparation of 12a in trans-6h, and cis-6h. The residue was purified by silica gel chromatography (petroleum ether/ethyl acetate, 5:1–2:1, v/v) to give the product.

trans-3-benzyl-5,6,7-trimethoxychroman-4-ol (trans-12h). colorless oil (6 mg, 36% yield); 1H NMR (400 MHz, CDCl3) δ 7.36–7.20 (overlapped, 5H), 6.17 (s, 1H), 4.70 (s, 1H), 3.99 (d, J = 7.8 Hz, 2H), 3.96 (s, 3H), 3.80 (s, 3H), 3.78 (s, 3H), 2.97 (dd, J = 13.8, 7.6 Hz, 1H), 2.68 (dd, J = 13.8, 7.9 Hz, 1H), 2.28–2.18 (m, 1H), 2.15 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 154.6, 152.0, 150.9, 139.6, 135.4, 129.2, 129.2, 128.7, 128.7, 126.4, 110.6, 95.7, 65.1, 61.4, 61.1, 60.6, 56.0, 40.2, 33.1; HRMS (ESI): m/z [M + NH4]+ calcd for C19H26O5N+ 348.1805; found: 348.1806.

cis-3-benzyl-5,6,7-trimethoxychroman-4-ole (cis-12h). colorless oil (13.1 mg, 40% yield); 1H NMR (400 MHz, CDCl3) δ 7.31 (t, J = 7.4 Hz, 2H), 7.24 (d, J = 7.2 Hz, 1H), 7.20 (d, J = 7.7 Hz, 2H), 6.25 (s, 1H), 4.61 (s, 1H), 4.11 (dd, J = 11.0, 2.0 Hz, 1H), 3.99 (s, 3H), 3.93 (dd, J = 10.9, 2.4 Hz, 1H), 3.84 (s, 3H), 3.81 (s, 3H), 2.65 (dd, J = 13.7, 6.9 Hz, 1H), 2.54 (overlapped, 2H), 2.22 (ddd, J = 9.2, 6.6, 2.9 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 154.4, 152.5, 150.6, 139.4, 135.6, 129.2, 129.2. 128.5, 128.5, 126.3, 109.1, 95.9, 64.4, 63.1, 61.3, 61.0, 55.89, 40.5, 34.6; HRMS (ESI): m/z [M + NH4]+ calcd for C19H26O5N+ 348.1805; found: 348.1803.

trans-2-benzyl-1-(2,3,4-trimethoxyphenyl)propane-1,3-diol (trans-12c). yellow oil (6.8 mg, 41% yield); 1H NMR (400 MHz, CDCl3) δ 7.26 (overlapped, 2H), 7.20–7.11 (m, 4H), 6.70 (d, J = 8.6 Hz, 1H), 4.96 (t, J = 4.8 Hz, 1H), 3.86 (s, 3H), 3.85 (s, 3H), 3.83 (s, 3H), 3.78 (d, J = 11.1 Hz, 1H), 3.57 (d, J = 11.1 Hz, 1H), 3.04 (d, J = 4.9 Hz, 1H), 2.78 (s, 1H), 2.74 (dd, J = 13.9, 5.9 Hz, 1H), 2.60 (dd, J = 13.8, 9.3 Hz, 1H), 2.20 (ddd, J = 8.7, 5.8, 2.8 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 153.3, 151.0, 142.0, 140.4, 129.2, 129.2, 128.8, 128.5, 128.5, 126.1, 121.8, 107.3, 73.6, 63.7, 61.1, 60.9, 56.1, 47.4, 34.9; HRMS (ESI): m/z [M + Na]+ calcd for C19H24O5Na+ 355.1516; found: 355.1515.

cis-2-benzyl-1-(2,3,4-trimethoxyphenyl)propane-1,3-diol (cis-12c). yellow oil (10.9 mg, 33% yield); 1H NMR (400 MHz, CDCl3) δ 7.23 (d, J = 7.4 Hz, 2H), 7.15 (t, J = 9.0 Hz, 4H), 6.71 (d, J = 8.7 Hz, 1H), 5.19 (d, J = 5.2 Hz, 1H), 3.93 (s, 3H), 3.87 (s, 6H), 3.56 (dd, J = 11.2, 2.6 Hz, 1H), 3.51 (dd, J = 11.2, 4.1 Hz, 1H), 2.92 (s, 1H), 2.88 (dd, J = 13.7, 3.6 Hz, 1H), 2.74 (dd, J = 13.5, 11.1 Hz, 1H), 2.31 (s, 1H), 2.10–2.01 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 153.1, 150.6, 141.9, 141.1, 129.3, 129.3, 128.5, 128.4, 128.4, 125.9, 121.8, 107.4, 72.3, 63.1, 61.3, 60.9, 56.1, 48.7, 31.4; HRMS (ESI): m/z [M + Na]+ calcd for C19H24O5Na+ 355.1516; found: 355.1512.

4.9 Procedure for preparation of 16

To a solution of trans-12h or cis-12h (1.0 equiv) in dry benzene (0.05 M), then pTSA (5 mol%) was added at 0 ℃. The reaction was sealed and stirred at room temperature for 2 h. The reaction was quenched with NaHCO3 saturated aqueous solution, and was extracted with ethyl acetate. The combined organic layer was dried over Na2SO4, filtered, and concentrated to give the crude product that was further purified by flash column chromatography on silica gel (petroleum ether/dichloromethane/ethyl acetate/ethyl acetate, 80:10:2, v/v) to afford 16.

3-benzyl-5,6,7-trimethoxy-2H-chromene (16). colorless oil (1.1 mg, quantitative yield); 1H NMR (400 MHz, CDCl3) δ 7.30 (d, J = 6.9 Hz, 2H), 7.24 (d, J = 6.3 Hz, 3H), 6.45 (s, 1H), 6.19 (s, 1H), 4.53 (s, 2H), 3.88 (s, 3H), 3.80 (s, 6H), 3.46 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 153.2, 149.1, 149.4, 137.9, 130.5, 128.8, 128.8, 128.6, 128.6, 126.6, 115.3, 109.5, 95.9, 67.8, 61.5, 61.1, 56.0, 40.3, 32.0; HRMS (ESI): m/z [M + H]+ calcd for C19H21O4+ 313.1434; found: 313.1435.

4.10 Procedure for preparation of 11h

The contents of a reaction tube charged with a solution of 7h (1.0 equiv), H3PO4 (50 mol%) in freshly distilled dichloromethane (0.05 M) were stirred for 12 h at 80 ℃. The reaction was quenched with NaHCO3 saturated aqueous solution, and was extracted with dichloromethane. The combined organic layer was dried over Na2SO4, filtered, and concentrated to give the crude product that was further purified by flash column chromatography on silica gel (petroleum ether/dichloromethane/ethyl acetate, 10:10:2, v/v) to afford 11h.

(trans-1-(6-bromo-2,3,4-trimethoxyphenyl)-2,3-dihydro-1H-inden-2-yl)methanol (11h