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

Participants

Reaction Steps

To a solution of 3,4-diethoxybenzoic acid (0.11 g; 0.52 mmol), and the product of Step A (0.09 g; 0.51 mmol) in anhydrous THF (2 ml), PyBroP (0.25 g; 0.54 mmol) was added followed by DIPEA (0.21 ml; 1.22 mmol), with stirring, at room temperature under N2. After 2 h of stirring, the mixture was diluted to 15 ml with EtOAc, washed with saturated NH4Cl (2×5 ml), brine, dried over anhydrous MgSO4 and filtered. The filtrate was evaporated to dryness under reduced pressure and the residue was suspended in anhydrous toluene (10 ml). To it 1M TBAF in THF (0.5 ml) was added and the reaction mixture was refluxed for 3 h under N2, cooled to room temperature and solvents were removed under reduced pressure. The residue was washed with H2O (5 ml) and the solid was purified by FCC (SiO2; CH2Cl2) to give the title compound (0.06 g; 34%) as colourless solid. 1H-NMR (CDCl3) 1.5 (m, 6H); 4.16-4.26 (m, 4H); 6.98 (d, 1H, J=8.5 Hz), 7.31-7.37 (m, 3H); 7.54 (d, 1H, J=8.1 Hz); 7.74 (d, 1H, J=2 Hz); 7.83 (d, 1H, J=8.4 Hz); 8.06 (dd, 1H, J=2, 8.4 Hz); 8.42 (s, 1H).

Provenance & Evidence