A solution of (S)-2-(4-chlorophenyl-α-methyl-3H-imidazo[4,5-b]pyridine-3-acetic acid (5.0 g, 0.0166 mole), 1,1'-carbonyldiimidazole (3.21 g, 0.0198 mole) and dry tetrahydrofuran (100 ml) was stirred at room temperature for 3 hours with nitrogen bubbling through it. A solution of dipropylamine (5.04 g, 0.050 mole) in tetrahydrofuran (7 ml) was added and the solution was heated at 50° C. overnight under nitrogen. The solvents were evaporated under reduced pressure and the resulting oil was partitioned between ethyl acetate (50 ml) and water (50 ml). The layers were separated and the aqueous layer was re-extracted with ethyl acetate (50 ml). The combined organic layers were washed once with water (50 ml) followed by two (50 ml) portions of 5% potassium hydroxide solution and then by water again (50 ml). The organic layer was dried over magnesium sulfate, charcoaled, filtered and evaporated to an oil which was crystallized from hot isopropyl ether. The solid was collected by filtration, and dried under high vacuum at room temperature to give 3.33 g (52%) of title compound, mp 96°-99° C.
