3,4-Diethoxybenzoic acid → 5-(3,4-Diethoxyphenyl)-3-(1H-indol-5-yl)-1,2,4-oxadiazole

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Reaction Steps

To a solution of 3,4-diethoxybenzoic acid (0.11 g; 0.52 mmol), and the product of Example 7, Step C (0.09 g; 10.52 mmol) in anhydrous THF (2 ml), PyBroP (0.25 g; 0.53 mmol) was added, followed by DIPEA (0.21 ml; 1.2 mmol), with stirring, at room temperature under N2. After overnight stirring, the mixture was diluted to 15 ml with EtOAc, washed with saturated NH4Cl (3×5 ml), brine, dried over anhydrous MgSO4 and filtered. The filtrate was evaporated to dryness under reduced pressure and the residue was purified by FCC (SiO2, EtOAc) to give the coupling product. This was suspended in anhydrous toluene (3 ml) and 1M TBAF was added. The resulting mixture was refluxed for 1 h under N2, cooled to room temperature and diluted to 15 ml with EtOAc, washed with H2O, brine, dried over anhydrous MgSO4, filtered and filtrate evaporated to dryness. The residue was purified by crystallization from MeOH, to give the title compound (0.096 g; 53%), as a colourless solid. 1H-NMR (CDCl3) 1.5 (m, 6H); 4.19 (m, 4H); 6.66 (s, 1H); 6.98 (d, 1H, J=8.4 Hz); 7.26 (m, 1H); 7.47 (d, 1H, J=8.5 Hz); 7.71 (d, 1H, J=1.8 Hz); 7.8 (dd, 1H, J=1.8, 8.5 Hz); 8.0 (dd, 1H, J=1.3, 8.5 Hz); 8.37 (broad s, 1H); 8.5 (s, 1H).

Provenance & Evidence