Tetrabutylammonium Fluoride → 2-Methylbenzofuran-5-carbonitrile

A mixture of the product of Step B (0.16 g; 1.02 mmol) and 1M TBAF in THF (0.1 ml) in dioxane (3 ml) was refluxed for 1 h under N2. After cooling to room temperature the solvents were removed under reduced pressure and the residue was filtered through a small pad of SiO2, washed with fresh CH2Cl2 (3×15 ml). The combined organic phase was evaporated to dryness to give 2-methylbenzofuran-5-carbonitrile (0.16 g; 100%), as greyish solid. This was dissolved in dioxane (5 ml) and KOH (0.2 g; 3.6 mmol) was added, followed by H2O (1 ml). The resulting mixture was refluxed overnight, cooled to room temperature and solvents were removed under reduced pressure. The residue was diluted to 1 ml with H2O. The insoluble material was filtered off, washed with fresh H2O, and combined filtrates were acidified to pH˜5 with concentrated citric acid. The solid formed was filtered off, dissolved in EtOAc (10 ml), dried over anhydrous MgSO4, filtered and filtrate evaporated to dryness to give title compound (0.08 g; 44%) as creamy solid. 1H-NMR (CDCl3) 2.47 (s, 3H); 6.42 (s, 1H); 7.43 (d, 1H, J=8.6 Hz); 7.99 (dd, 1H, J=1.6, 8.6 Hz); 8.26 (d, 1H, J=1.6 Hz).