Propanal → 2,4-Dimethyl-6-oxo-1-propylamino-1,6-dihydro-pyridine-3-carboxylic acid methyl ester

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A mixture of 1-amino-2,4-dimethyl-6-oxo-1,6-dihydro-pyridine-3-carboxylic acid methyl ester (2.8 g, 14 mmol), propionaldehyde (5.1 mL, 71 mmol) and molecular sieves (size 4 Å, 5 g) in methanol (50 mL) was stirred overnight at room temperature. The solution was cooled to 5° C. and sodium tetrahydroborate (2.2 g, 57 mmol) was added in small portions. It was stirred for 1 hour at 5° C., then filtered and evaporated. The residue was partitioned between water (100 mL) and ethyl acetate (3×100 mL). The combined organic solution was dried (MgSO4) and evaporated. The residue was treated with hot n-heptane, cooled to 10° C. and the unreacted starting material was removed by filtration. The heptane solution was purified by flash chromatography to give the title compound. LC-MS (m/z) 239.1 (MH+); tR=1.20 (method C). 1H NMR (600 MHz, CDCl3): 1.01 (t, J=7.4 Hz, 3H, Me of Pr), 1.61 (sextet, J=7.3 Hz, 2H, CH2 of Pr), 2.19 (d, J=0.9 Hz, 3H, Me), 2.53 (s, 3H, Me), 2.56-3.1 (very br. coalescing d, 2H, CH2N), 3.87 (s, 3H, OMe), 5.92 (t, J=7.3 Hz, 1H, NH), 6.35 (s, 1H, C5-H).

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