A mixture of (1-benzylpiperidin-3-yl)(5-chloro-1-(triisopropylsilyl)-1H-pyrrolo[2,3-b]pyridin-4-yl)methanone (1.45 g, 2.84 mmol), anhydrous hydrazine (0.273 g, 8.53 mmol) and AcOH (0.163 mL, 2.84 mmol) was heated in EtOH (35 mL) at reflux for about 16 h. The reaction mixture was cooled to room temperature, the solvent was removed under reduced pressure and the residue partitioned between saturated aqueous NaHCO3 (50 mL) and EtOAc (60 mL). The organic phase was washed with brine (40 mL) and concentrated to yield 4-((1-benzylpiperidin-3-yl)(hydrazono)methyl)-5-chloro-1H-pyrrolo[2,3-b]pyridine (1.04 g, quantitative) as a brown amorphous solid that was used directly in the next step without further purification: LC/MS (Table 2, Method a) Rt=1.57 min; MS m/z: 368 (M+H)+.
