[Cl-].[Br-].ClC1N=C2N=C(CCC)NC2=C(C)C=1.Br.[Br:18][C:19]1[N:24]=[C:23]2[N:25]=[C:26]([CH2:28][CH2:29][CH3:30])[NH:27][C:22]2=[C:21]([CH3:31])[CH:20]=1.[H-].[Na+].[CH2:34](Br)[C:35]1[CH:40]=[CH:39][CH:38]=[CH:37][CH:36]=1>C(O)(=O)C.CN(C=O)C>[CH2:34]([N:25]1[C:23]2=[N:24][C:19]([Br:18])=[CH:20][C:21]([CH3:31])=[C:22]2[N:27]=[C:26]1[CH2:28][CH2:29][CH3:30])[C:35]1[CH:40]=[CH:39][CH:38]=[CH:37][CH:36]=1
7-Methyl-2-propylimidazo[4,5-b]pyridine-5-carboxylic acid or the 2-ethyl analog is prepared from 7-methyl-2-propylimidazo[4,5-b]pyridine or the 2-ethyl analog by treatment with m-chloroperoxybenzoic acid to obtain the N-oxide which is then treated with POCl3 to give 5-chloro-7-methyl-2-propylimidazo-[4,5-b]pyridine or 2-ethyl analog. The chloride is then exchanged for a bromide by reaction of 5-chloro-7-methyl-2-propylimidazo[4,5-b]pyridine or the 2-ethyl analog with HBr in acetic acid. The resulting 5-bromo-7-methyl-2-propylimidazo[4,5-b]pyridine or 2-ethyl analog is treated with NaH in DMF followed by benzyl bromide to obtain 3-benzyl-5-bromo-7-methyl-2-propylimidazo[4,5-b]pyridine or its corresponding 2-ethyl analog which is in turn treated with CuCN in hot pyridine to obtain 3-benzyl-5-cyano-7-methyl-2-propylimidazo[4,5-b]pyridine or the corresponding 2-ethyl analog. The cyano compound is hydrolyzed to 3-benzyl-7-methyl-2-propylimidazo[ 4,5-b]pyridine-5-carboxylic acid or the corresponding 2-ethyl analog by treatment with H2SO4 --H2O. This acid is esterified by reaction with MeOH--HCl. The benzyl group is removed by hydrogenation at 1 atm. in MeOH-HCl solution using Pd(OH)2 as catalyst. This compound can be alkylated as described earlier and the product methyl ester is converted to the carboxylic acid by treatment with hydroxide.
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