(R)-tert-butyl 3-((5-tosyl-5H-pyrrolo[2,3-b]pyrazin-2-yl)methylcarbamothioyl)piperidine-1-carboxylate → (R)-tert-butyl 3-(6-tosyl-6H-imidazo[1,5-a]pyrrolo[2,3-e]pyrazin-1-yl)piperidine-1-carboxylate

To a solution of (R)-tert-butyl 3-((5-tosyl-5H-pyrrolo[2,3-b]pyrazin-2-yl)methylcarbamothioyl)-piperidine-1-carboxylate (5.61 g, 10.3 mmol) in 1,4-dioxane (96 mL) was added mercury (II) trifluoroacetate (4.38 g, 10.3 mmol) and the reaction mixture was stirred at ambient temperature for about 2 h then filtered through a pad of Celite®. The Celite® pad was rinsed with EtOAc (50 mL) and the filtrate was concd under reduced pressure. The crude residue was dissolved in EtOAc (40 mL) and the organic phase was washed with saturated aqueous NaHCO3 (2×40 mL), brine (30 mL), dried over anhydrous MgSO4, filtered, and concd under reduced pressure. The crude material was purified by silica gel chromatography eluting with a gradient of 0-5% MeOH in DCM to afford (R)-tert-butyl 3-(6-tosyl-6H-imidazo[1,5-a]pyrrolo[2,3-e]pyrazin-1-yl)piperidine-1-carboxylate (4.4 g, 87%): LC/MS (Table 1, Method b) Rt=2.49 min; MS m/z: 496 (M+H)+.