Ethanol → [5-(2-Amino-phenyl)-thiophen-2-yl]-acetic acid methyl ester

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(The following reaction is carried out in an N2 atmosphere.) Ethanol (3.7 mL), tetrakis-(triphenylphosphine)-palladium(0) (289 mg, 0.25 mmol) and Na2CO3 decahydrate (4.0 g, 14.0 mmol) dissolved in water (5.2 mL) are subsequently added to a solution of 2-amino-benzeneboronic acid hydrochloride (910 mg, 5.25 mmol) in toluene (52 mL). Degas the reaction mixture carefully (5 times) and flush with N2 again. A solution of (5-bromo-thiophen-2-yl)-acetic acid methyl ester (43) (1.17 g, 5.0 mmol) in toluene (4.5 mL) is added. Degas the mixture again (5 times) and stir for 22 h at 100° C. Partition the reaction solution between EtOAc and brine and extract the separated aqueous layer with EtOAc (3 times). Wash combined organic layer with water and brine and dry it with Na2SO4. Purify the crude product by preparative radial chromatography (CyH/EtOAc 5+1] to obtain [5-(2-amino-phenyl)-thiophen-2-yl]-acetic acid methyl ester (44) as a brown oil (634 mg, 51%). 1H NMR (400 MHz, CDCl3): 3.73 (s, 3H); 3.83 (s, 2H); 3.92-4.07 (br.s, 2H); 6.74 (d, 1H); 6.76 (td, 1H, J1=7.6 Hz, J2=1.3 Hz); 6.92 (d, 1H, J=3.5 Hz); 7.02 (d, 1H, J=3.5 Hz); 7.11 (td, 1H, J1=7.6 Hz, J2=1.5 Hz); 7.23 (dd, 14H, J1=7.6 Hz, J2=1.5 Hz).

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