[Synthesis]
Tert-butyl 3-ethynylbenzoate (117) (1.50 g, 9.37 mmol) was dissolved in anhydrous dichloromethane (DCM) (70 mL) and trifluoroacetic acid (TFA) (35.9 mL, 488 mmol) was added slowly. The reaction mixture was stirred at room temperature for 3 hours and then concentrated under vacuum. Toluene was then added and concentrated again under vacuum to give a light yellow solid. The solid was dissolved in methanol (50 mL) and concentrated again. Concentrated sulfuric acid (about 1 mL) was added and the resulting solution was stirred at 85°C for 20 hours. After completion of the reaction, it was cooled to room temperature and the volatiles were removed under vacuum. The residue was diluted with ethyl acetate (EtOAc) (200 mL) and slowly neutralized with saturated aqueous sodium bicarbonate (NaHCO3) (100 mL). The organic and aqueous layers were separated and the aqueous layer was further extracted with ethyl acetate (200 mL). The organic layers were combined, washed sequentially with water (100 mL) and brine (100 mL), dried over anhydrous magnesium sulfate (MgSO4), filtered and concentrated in vacuo to afford methyl 3-alkynylbenzoate (131) (1.136 g, 96% overall yield in two steps) as a pale yellow solid. The product was confirmed by 1H NMR (400 MHz, CDCl3): δ 8.17 (t, J = 1.5 Hz, 1H), 8.03-8.00 (m, 1H), 7.66 (dt, J = 7.7, 1.4 Hz, 1H), 7.41 (td, J = 7.8, 0.4 Hz, 1H), 3.93 (s, 3H), 3.12 (s, 1H) . the LCMS analysis method C showed a retention time of 5.84 min. |