General procedure for the synthesis of 3-(4,5-dihydro-2-oxazolyl)-pyridine from 3-pyridinecarboxaldehyde and 2-aminoethanol: To a solution of 3-pyridinecarboxaldehyde (79 mg, 0.5 mmol), 2-aminoethanol (200 μL, 3.2 mmol), and pyridine (80 μL, 1.0 mmol) in methanol (6 mL) was added PTAB (trimethylphenyltrimethyl ammonium trimethylammonium tribromide, 376 mg, 1.0 mmol). The reaction mixture was stirred at room temperature for 22 hours and then treated with 0.5 M aqueous Na2S2O3 (10 mL) and 1.0 M aqueous NaHCO3 (15 mL), followed by extraction with EtOAc (60 mL). The organic layer was washed sequentially with 0.5 M Na2S2O3 aqueous solution and saturated NaCl aqueous solution and dried with MgSO4. After the solvent was removed under vacuum, the residue was purified by column chromatography on silica gel (Wako C-200), the eluent being a mixture of CCl4 and CCl4-CHCl3 (2:1 v/v) to afford 3-(4,5-dihydro-2-oxazolyl)-pyridine (85 mg) in 86% yield.
