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Stage #1: With sodium hydroxide In ethanol for 6 h; Reflux Stage #2: With hydrogenchloride In ethanol; water
General procedure: These were made by decarboxylation/Vilsmeier or hydrolysis/reduction/reoxidation as detailed below, unless otherwise stated.Decarboxylation was carried out by refluxing a solution of the ester (1 equiv) in 40percent aqueous H2SO4 (3 mL) for 18 h. The solution was then cooled in ice and neutralised to pH 7 with 6 M NaOH, then extracted twice with CH2Cl2. The combined extracts were dried (Na2SO4) and the solvent removed in vacuo to leave the decarboxylated material. The pyrazolo[1,5-a]pyridine was then reacted under Vilsmeier conditions in dry DMF (2 mL) with POCl3 (3 equiv) at 0 °C under an atmosphere of N2. The reaction mixture was then warmed to room temperature and stirred for 2 h. The solution was poured onto ice, basified to pH 10 with 1 M NaOH, stirred for 1 h then extracted twice with CH2Cl2. The combined extracts were washed twice with water, dried (Na2SO4) and the solvent removed in vacuo to leave the aldehyde.Alternatively, the ester was hydrolysed by refluxing a solution of the ester (1 equiv) in 1 M NaOH (3 equiv) and EtOH (5 mL) for 6 h. The EtOH was removed in vacuo, and then the aqueous residue acidified to pH 1 with 1 M HCl. The precipitated carboxylic acid was filtered off, washed with water and dried. The carboxylic acid was reduced by adding CDI (1.5 equiv) to a suspension of carboxylic acid (1 equiv) in dry THF (10 mL) under an atmosphere of N2. After stirring for 18 h, the resulting solution was added dropwise to a solution of NaBH4 (5 equiv) in H2O (10 mL) and stirred for 30 min. The reaction was then quenched by the addition of 1 M HCl and stirred for a further 30 min. The solution was neutralised with saturated aqueous NaHCO3 and extracted twice with CH2Cl2. The combined organic layers were dried (Na2SO4) and the solvent removed in vacuo. Chromatography (eluting with a hexanes: EtOAc gradient) gave the alcohol. Reoxidation was carried out by stirring a suspension of the pyrazolo[1,5-a]pyridine-3-methanol (1 equiv) and MnO2 (10 equiv) in CH2Cl2 (2 mL) at room temperature for 4 days. The reaction mixture was then filtered through celite, washed with CH2Cl2, and the solvent removed from the filtrate in vacuo to leave the aldehyde.
Reference：
[1] Bioorganic and Medicinal Chemistry, 2012, vol. 20, # 1, p. 69 - 85
2
[ 127717-19-5 ]
[ 143803-93-4 ]
Reference：
[1] Bioorganic and Medicinal Chemistry Letters, 2009, vol. 19, # 21, p. 6122 - 6126
3
[ 108-99-6 ]
[ 143803-93-4 ]
Reference：
[1] Bioorganic and Medicinal Chemistry, 2012, vol. 20, # 1, p. 69 - 85
General procedure: These were made by decarboxylation/Vilsmeier or hydrolysis/reduction/reoxidation as detailed below, unless otherwise stated.Decarboxylation was carried out by refluxing a solution of the ester (1 equiv) in 40% aqueous H2SO4 (3 mL) for 18 h. The solution was then cooled in ice and neutralised to pH 7 with 6 M NaOH, then extracted twice with CH2Cl2. The combined extracts were dried (Na2SO4) and the solvent removed in vacuo to leave the decarboxylated material. The pyrazolo[1,5-a]pyridine was then reacted under Vilsmeier conditions in dry DMF (2 mL) with POCl3 (3 equiv) at 0 C under an atmosphere of N2. The reaction mixture was then warmed to room temperature and stirred for 2 h. The solution was poured onto ice, basified to pH 10 with 1 M NaOH, stirred for 1 h then extracted twice with CH2Cl2. The combined extracts were washed twice with water, dried (Na2SO4) and the solvent removed in vacuo to leave the aldehyde.Alternatively, the ester was hydrolysed by refluxing a solution of the ester (1 equiv) in 1 M NaOH (3 equiv) and EtOH (5 mL) for 6 h. The EtOH was removed in vacuo, and then the aqueous residue acidified to pH 1 with 1 M HCl. The precipitated carboxylic acid was filtered off, washed with water and dried. The carboxylic acid was reduced by adding CDI (1.5 equiv) to a suspension of carboxylic acid (1 equiv) in dry THF (10 mL) under an atmosphere of N2. After stirring for 18 h, the resulting solution was added dropwise to a solution of NaBH4 (5 equiv) in H2O (10 mL) and stirred for 30 min. The reaction was then quenched by the addition of 1 M HCl and stirred for a further 30 min. The solution was neutralised with saturated aqueous NaHCO3 and extracted twice with CH2Cl2. The combined organic layers were dried (Na2SO4) and the solvent removed in vacuo. Chromatography (eluting with a hexanes: EtOAc gradient) gave the alcohol. Reoxidation was carried out by stirring a suspension of the pyrazolo[1,5-a]pyridine-3-methanol (1 equiv) and MnO2 (10 equiv) in CH2Cl2 (2 mL) at room temperature for 4 days. The reaction mixture was then filtered through celite, washed with CH2Cl2, and the solvent removed from the filtrate in vacuo to leave the aldehyde.
General procedure: These were made by decarboxylation/Vilsmeier or hydrolysis/reduction/reoxidation as detailed below, unless otherwise stated.Decarboxylation was carried out by refluxing a solution of the ester (1 equiv) in 40% aqueous H2SO4 (3 mL) for 18 h. The solution was then cooled in ice and neutralised to pH 7 with 6 M NaOH, then extracted twice with CH2Cl2. The combined extracts were dried (Na2SO4) and the solvent removed in vacuo to leave the decarboxylated material. The pyrazolo[1,5-a]pyridine was then reacted under Vilsmeier conditions in dry DMF (2 mL) with POCl3 (3 equiv) at 0 C under an atmosphere of N2. The reaction mixture was then warmed to room temperature and stirred for 2 h. The solution was poured onto ice, basified to pH 10 with 1 M NaOH, stirred for 1 h then extracted twice with CH2Cl2. The combined extracts were washed twice with water, dried (Na2SO4) and the solvent removed in vacuo to leave the aldehyde.Alternatively, the ester was hydrolysed by refluxing a solution of the ester (1 equiv) in 1 M NaOH (3 equiv) and EtOH (5 mL) for 6 h. The EtOH was removed in vacuo, and then the aqueous residue acidified to pH 1 with 1 M HCl. The precipitated carboxylic acid was filtered off, washed with water and dried. The carboxylic acid was reduced by adding CDI (1.5 equiv) to a suspension of carboxylic acid (1 equiv) in dry THF (10 mL) under an atmosphere of N2. After stirring for 18 h, the resulting solution was added dropwise to a solution of NaBH4 (5 equiv) in H2O (10 mL) and stirred for 30 min. The reaction was then quenched by the addition of 1 M HCl and stirred for a further 30 min. The solution was neutralised with saturated aqueous NaHCO3 and extracted twice with CH2Cl2. The combined organic layers were dried (Na2SO4) and the solvent removed in vacuo. Chromatography (eluting with a hexanes: EtOAc gradient) gave the alcohol. Reoxidation was carried out by stirring a suspension of the pyrazolo[1,5-a]pyridine-3-methanol (1 equiv) and MnO2 (10 equiv) in CH2Cl2 (2 mL) at room temperature for 4 days. The reaction mixture was then filtered through celite, washed with CH2Cl2, and the solvent removed from the filtrate in vacuo to leave the aldehyde.
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