To a solution of (R)-ethyl 1-(5,6-diaminopyridin-2-yl)piperidine-3-carboxylate (250 mg, 0.686 mmol) in ethanol (15 mL) was added 6-cyclopropylpicolinaldehyde (55 mg, 0.823 mmol), sulfur (43 mg, 1.372 mmol) and acetic acid (1.5 mL) at room temperature. The reaction mixture was stirred at 80° C. for 18 h. The reaction mixture was poured into ice water and extracted with ethyl acetate. The organics were concentrated under reduced pressure and the crude material was purified via preparative TLC (80% ethyl acetate in petroleum ether) to afford (R)-ethyl 1-(2-(6-cyclopropylpyridin-2-yl)-3H-imidazo[4,5-b]pyridin-5-yl)piperidine-3-carboxylate (180 mg). MS (ES+APCI) (M+H) 392.2; LCMS retention time 3.757 min (Method J).
