l-(2,4-Dichlorobenzyl)-lH-pyrazolor3,4blpyridine-3-carboxylic Acid
lH-Pyrazolo[3,4b]pyridine-3-carboxylic acid methyl ester (8 g, 0.0452 mol) was suspended in acetonitrile (200 mL) and the resulting suspension was stirred under heating for 10 min. in order to homogenize the solution. Potassium carbonate (31.2 g, 0.226 mol) was then added in one lot, followed by the addition of the tetrabutylammonium iodide (0.08 g, catalytic) and 2,4-dichlorobenzyl chloride (10.6 g, 0.0543 mol). The reaction mixture was heated to reflux for 2 h under good stirring. The reaction progress was monitored by TLC. After completion of the reaction, the mixture was cooled to room temperature and potassium carbonate was filtered off. Acetonitrile was distilled off under reduced pressure to afford the crude benzylated product. The crude product was purified using column chromatography (silica gel, eluent started with hexane then 8:2 hexane/ethyl acetate) to yield the pure product as white crystals (11 g, 73%) mp 135-136 0C.
1H NMR (CDCl3) 8.04 (dd, J = 4. 5 and 1.6 Hz, 1 H), 8.58 (dd, J = 8.1 and 1.6 Hz, 1 H), 7.45 (d, J = 2.0 Hz, 1 H), 7.36 (dd, J = 8.1 and 4.5 Hz, 1 H), 7.10 (dd, J = 8.3 and 2.0 Hz, 1 H), 6.72 (d, J = 8.3 Hz, 1 H ), 5. 92 (s, 2 H), 4.06 (s, 3 H).
MS (FAB) m/z: 336 (M++ 1).
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