An isopropanolic solution of i-PrONa, obtained by dissolving of sodium (0.082 g, 3.57 mmol, 1 equiv.) in i-PrOH (75 ml), was treated with methyl[(4Z)-1-methyl-5-oxo-4-{1-[(pyridin-2-ylmethyl)amino]pentylidene}-4,5-dihydro-1H-pyrazol-3-yl]acetate (Compound of Formula (VIII) (0.61 g, 3.57 mmol, 1 equiv.). The reaction mixture was refluxed for 1 h, then cooled and neutralized to pH 7 by addition of 0.59 ml of a 20% aqueous HCl solution. 50 ml of i-PrOH were removed in vacuo and 25 ml of H2O were added before placing the flask in the fridge overnight. The white precipitate formed was filtered off, washed with water (2×5 ml), then with cyclohexane and dried in vacuo. 0.88 g of pure product 4-butyl-2-methyl-5-(pyridin-2-ylmethyl)-1H-pyrazolo[4,3-c]pyridine-3,6(2H,5H)-dione was obtained. Yield 80%. 1HNMR (DMSO-d6, 400 MHz): 0.80 (3H, t, J=7.2 Hz); 1.29-1.35 (2H, m); 1.38-1.43 (2H, m); 3.19 (3H, s); 3.22-3.24 (2H, m); 5.49 (2H, s); 5.72 (1H, s); 7.42 (1H, d, J=8 Hz); 7.62 (1H, t, J=6.6 Hz); 8.12 (1H, t, J=8 Hz); 8.65 (1H, d, J=5.2 Hz). MS (ESI+): 313.4; MS (ESI−): 311.3.
