Acetic acid, 2-(triphenylphosphoranylidene)-, ethyl ester → (E)-3-(3-isopropoxy-4-methoxy-phenyl)-acrylic acid ethyl ester

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Reaction Steps

A mixture of 3-isopropoxy4-methoxy-benzaldehyde (3.9 g, 20 mmol) and (ethoxycarbonylmethylene)triphenylphosphorane (6.96 g. 20 mmol) in toluene (100 ml) is heated at reflux for 2 hours, cooled to ambient temperature and evaporated. The crude product is taken in to dichloromethane and eluted through a pad of, silica to afford (E)-3-(3-isopropoxy-4-methoxy-phenyl)-acrylic acid ethyl ester, TLC Rf 0.70 (1:1 hexane-ethyl acetate). This intermediate is dissolved in nitromethane (10 ml), 1,1,3,3-tetramethylguanidine (0.5 ml) is added and the reaction heated at 70° C. for 36 hours. The solvent is evaporated, the residue is taken into ethyl acetate and washed with 2N aqueous HCl, water and brine. After drying over sodium sulfate and evaporation, the crude product is purified by flash column chromatography (4:1 hexane-ethyl acetate elution) to afford 3-(3-isopropoxy-4-methoxy-phenyl)-4-nitro-butyric acid ethyl ester, 1H NMR (400 MHz, CDCl3) δ 1.20 (t J 7 3H), 1.38 (d J 7 6H), 2.75 (d J 6 2H), 3.90 (m 1H), 4.10 (m 2H), 4.48-4.78 (m 3H), 6.75-6.86 (m 3H). This intermediate is converted into [1-(3,5-diisopropoxy-phenyl)-6-isopropoxy-7-methoxy-isoquinolin-4-yl]-acetic acid using the general procedure for Intermediate 20. Characterised as the ethyl ester, [MH]+ 496.

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