Photo-Oxidation of Substituted 2-Dicyanomethylene-1,2-dihydropyridines

References

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• To methanol (20 ml) containing 5% aqueous sodium hydroxide (1 ml) was added 2a (292 mg, 1 mmol). The mixture was stirred at r.t. for 2 h., and then was poured over water (80 ml). The mixture was acidified until pH=2 by 5% hydrochloric acid. The precipitate formed was collected and recrystallized from 2-propanol. Yield 251 mg (95%), mp 212–220 °C (dec.), i.r. (KBr), 3412, 3324,3206, 2236,1759, 1641, 1568,1396, 1284 cm-1, 1H-nmr (DMSO-d6), δ 2.8–4 (br, 1H), 7.58 (s, 5H), 8.30 (s, 2H). Anal., Calcd. for C14H8N4O2, C, 63.64, H, 3.05, N, 21.20. Found, C, 63.39, H, 3.16, N, 21.53
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• A solution of 6-amino-3,4-dicyano-4-phenyl-2-pyridincarboxylic acid (264 mg, 1 mmol) in DMSO (20 ml) was heated under reflux with stirring for 2 h., and then was poured over water (150 ml) acidified by hydrochloric acid. The precipitate formed was separated and the filtrate was extracted with chloroform and concentrated in vacuo. Both solids, the precipitate and the residue obtained by concentration of the chloroformic extracts, were chromatographed on a silica gel column. The elution with hexaneethylacetate 6,4 gave 170 mg of the 2-amino-3,5-dicyane-4-phenylpyridine. Yield (77 %), mp. 247–248 °C from ethanol, i.r. (KBr), 3420–3300, 3140, 2220, 1655, 1620, 1580, 1565, 1530, 1485, 1345, 1255, 1230 cm-1, 1H-NMR (DMSO-d6), δ 7.38 (s, 5H), 7.75 (br. s, 2H), 8.42 (s, 1H). Anal. Calcd. for C13H8N4, C, 70.89, H, 3.66, N, 25.44. Found, C, 71.15, H, 3.50, N, 25.35
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• To a solution of 2a (0.58 g, 2 mmol) in ethanol (50 ml) hydrochloric acid (15 ml, 10 N) was added. The mixture was heated under reflux with stirring for 10 h. The precipitate formed was collected and recrystallized from methanol and drops of acetone affording 0.42 g of 2-amino-3-cyano-4-phenylpyrrol (3,4-b)pyridin-5,7-dione. Yield (80 %). mp. 339–341 °C, i.r. (KBr) 3460, 3300–3170, 2215, 1765, 1710, 1600, 1545, 1485, 1370, 1325. 1H-NMR (DMSO-d6) 8, 7.54 (s, 5H), 8.20 (br. s, 2H), 11.40 (s, 1H), Anal. Calcd. for C14H∗∗∗N4O2, C, 63.64, H, 3.05, N, 21.20. Found, C, 63.30, H, 2.97, N, 21.10
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