1) By reduction of 2-(5-oxo-5H[1]benzopyrano[2,3-b]pyridin-7-yl)propionic acid (I) with NaBH4 in basic water. 2) By treating with CO2 the Grignard compound prepared from 7-(1-bromoethyl)-5H[1]benzopyrane[2,3-b]pyridine (II) with Mg in THF. 3) By oxidation of 2-(5H[1]benzopyrane[2,3b]pyridin-7-yl)propionaldehyde (III) with silver oxide in basic ethanol. 4) By reduction of 2-(5H[1]benzopyrane[2,3-b]pyridin-7-yl)acrylic acid (IV) or 2-(5H[1]benzopyrane[2,3b]pyridin-7-yl)-2-chloropropionic acid (V) with H2 over Raney-Ni in aqueous NaOH.
1) By cyclization of 2-[p-(alpha-carboxyethyl)phenoxy]nicotinic acid (XIII) with phosphoric acid at 130-40 C. 2) By cyclization of 2-[3-(2-chloronicotinoyl)-4-hydroxyphenyl]propionic acid (XIV) hy means of Cu - Cu2I2 in aqueous NaOH. 3) By oxidation of 2-(5-oxo-5H[1]benzopyrano[2,3-b]-pyridin-7-yl)propionaldehyde (XV) with KMnO4 in pyridine-water.
The bromination of 7-methyl-5-oxo-5H[1]benzopyrane[2,3-b]pyridine (XVI) with NBS in CCl4 gives 7-bromomethyl-5-oxo-5H[1]benzopyrane[2,3-b] pyridine (XVII), which is treated with NaCN in DMF yielding 7-cyanomethyl-5-oxo-5H[1]benzopyrane[2,3b]pyridine (XVIII). The reaction of (XVIII) with diethyl carbonate (A) by means of sodium ethoxide in ethanol affords ethyl 2-cyano-2-(5-oxo-5H[1]benzopyrane[2,3b]pyridine-7-yl)acetate (XIX), which, without isolation, is methylated with MeI giving ethyl 2-cyano-2-(5-oxo-5H[1]benzopyrane[2,3b]pyridine-7-yl)propionate (XX); finally this product is hydrolyzed and decarboxylated with dry HCl in refluxing acetic acid. An alternative way starting from the cyano derivative (XVIII) is its methylation with NaNH2 and MeI giving 7-(1-cyanoethyl)-5-oxo-5H[1]benzopyrane[2,3-b]pyridine (XXI), which is hydrolyzed with dry HCl in refluxing acetic acid.
The reduction of 5-oxo-5H[1]benzopyrane[2,3-b]pyridine (VI) affords 5-hydroxy-5H[1]benzopyrane[2,3-b]pyridine (VII), which is reduced again with refluxing isopropanol and HCl giving 5H[1]benzopyrane[2,3b]pyridine (VIII). This product is chloromethylated with HCHO and HCl in H2SO4 to yield 7-chloromethyl-5H[1]benzopyrane[2,3-b]pyridine (IX), which is treated with KCN in DMF-water to afford 7-cyanomethyl-5H[1]benzopyrane[2,3-b]pyridine (X). The reaction of (X) with diethyl carbonate (A) in ethanol containing sodium ethoxide gives ethyl 2-cyano-2-(5H[1]benzopyrano[2,3-b]pyridine-7-yl)acetate (XI), which, without isolation, is methylated with MeI to ethyl 2-cyano-2-(5H[1]-benzopyrano[2,3-b]pyridin-7-yl)propionate (XII). Finally, (XII) is hydrolyzed and decarboxylated with dry HCl in refluxing acetic acid.