To a solution of diethyl 1H-pyrrolo[2,3-b]pyridine-2,6-dicarboxylate (Intermediate D, 1.00 g, 3.81 mmol) in DMF (15 mL) cooled to 0° C. is added 60% sodium hydride in mineral oil (168 mg, 4.19 mmol). The mixture is stirred at 0° C. for 20 min after which a solution of tert-butyl 6-methyl-1,2,3-oxathiazinane-3-carboxylate 2,2-dioxide (1.05 g, 4.19 mmol) in DMF (2 mL) is added. After being stirred overnight, the mixture is concentrated under reduced pressure and the residue is partitioned between ethyl acetate and saturated NaHCO3 solution. The layers are separated and the aqueous layer is further extracted with ethyl acetate. The combined organic phases are washed with brine, and are dried (Na2SO4). The solvent is removed in vacuo and the crude material is purified via flash column chromatography using a gradient elution of 0-30% ethyl acetate/heptanes to afford the title compound as a yellow oil (1.20 g, 73%). LCMS: 434.89 (M+H+).
