To a −78° C. solution of 7-iodo-5-triisopropylsilanyl-2-(3,4,5-trimethoxy-phenyl)-5H-pyrrolo[2,3-b]pyrazine (680 mg, 1.2 mmol) in THF (4 mL) was added iPrMgCl.LiCl (2.7 mL, 1.3 M in THF, 3.5 mmol) dropwise along the side of the flask. The reaction was stirred for 10 min at −78° C. and a solution of 4-formyl-4-methyl-piperidine-1-carboxylic acid tert-butyl ester (700 mg, 3.1 mmol) in THF (4 mL) was added slowly along the side of the flask. The reaction was allowed to slowly warm to room temperature, stirred overnight, and partitioned between saturated NH4Cl and EtOAc. The aqueous phase was extracted with EtOAc and the combined organic phases were dried over Na2SO4 and concentrated to give a yellow oil. The crude product was purified by flash chromatography using 40 g of silica gel and 0-50% of 9.5:0.5 MeOH:conc NH4OH in CH2Cl2 as eluant to afford 950 mg of impure 4-{hydroxy-[5-triisopropylsilanyl-2-(3,4,5-trimethoxy-phenyl)-5H-pyrrolo[2,3-b]pyrazin-7-yl]-methyl}-4-methyl-piperidine-1-carboxylic acid tert-butyl ester. M+Na 691.
