Acetic Acid → 3-(3,4-Dimethoxyphenyl)-2-propenal

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In order to study the contribution of the length of the conjugation bridge to the AR activity, compound Q110 with a four-conjugated-double bond linker and compound Q111 with a five-conjugated-double bond linker were synthesized and illustrated in Scheme 13. Compound Q110 was synthesized starting from 1,2-dimethoxy-4-propyl-benzene. To a solution of 3-(3,4-dimethoxyphenyl) propane in dry dioxane was added with DDQ (3.1 eq.) and catalytic amount of acetic acid. The mixture was sonicated for 2 h with TLC monitoring. After completion of the reaction, the solid was filtered out and the filtration was concentrated. The residue was dissolved in EtOAc and washed with water, 2% NaHCO3, and brine. The organic extract was dried over Na2SO4 and concentrated to afford a crude as yellow-brownish solid, which was purified with neutral alumina column chromatography and eluted with hexanes-ethyl acetate mixture to give a light yellow solid, 3,4-dimethoxycinnamaldehyde in 60% yield (B. P. Joshi et al., Tetrahedron, 62, 2590-2593, 2006). A solution of 2,4-petanedione (3 eq.) and B2O3 (1 eq.) in EtOAc was stirred at 40° C. for 0.5 h, 3,4-dimethoxycinnamaldehyde (1 eq.) and tributyl borane (1 eq.) were added. The resulting reaction mixture was stirred at 40° C. for 0.5 h. Butylamine (1.2 eq.) in EtOAc was added dropwise at the temperature and stirred at 40° C. for 16 h. To the red reaction mixture, 1% HCl aq was added and the mixture was stirred to 60° C. for 1 h. After cooling to rt, the aqueous was separated and the organic was washed with water to pH˜7 and dried over Na2SO4. The crude was purified by silica gel flash column chromatography to get the intermediate product 8-(3,4-Dimethoxy-phenyl)-4-hydroxy-octa-3,5,7-trien-2-one as an off-white solid. A solution of the intermediate (1 eq.) and B2O3 (0.7 eq.) in EtOAc was stirred at 70° C. for 0.5 h. 3,4-dimethoxybenzaldehyde (1 eq.) and trubutyl borane (1 eq.) were added and the reaction mixture was stirred at 70° C. for 0.5 h. Piperidine (1.2 eq.) in EtOAc was added dropwise and the reaction mixture was stirred at 88-90° C. for 1 h. After cooling to 60° C., 1% HCl aq was added and the mixture was stirred at 60° C. for 0.5 h. The reaction mixture was worked-up by following the procedure described above and the crude was purified by silica gel column chromatography to afford the desired product Q110 as a red solid. Amorphous, mp. 65-68° C., ESI MS m/z: 423.1 [M+H]+; 1H NMR (300 MHz, CDCl3) δ: 7.64-7.58 (d, 2H, H-1 and 2), 7.16-7.02 (4H, aromatic ring H and trans double bond H), 6.90-6.82 (4H, aromatic ring H), 6.53-6.48 (1H, trans double bond H), 6.18-6.12 (1H, trans double bond H), 5.75 (s, 1H, H-4), 3.94-3.92 (12H, —OCH3).

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