N-2-trimethylsilylethyoxymethyl or N-SEM

Protection

To a flask was added NaH (60% in mineral oil, 0.473g, 11.8 mmol) and THF (59.1 mL). The mixture was cooled to about 0°C. 6-Nitro-1H-indazole-3-carbaldehyde (2.26g, 11.8 mmol) was added in several smaller portions and the mixture was stirred at about 0°C for 20 min. SEMCl (2.30mL, 13.0 mmol) was added dropwise and the mixture was stirred at about 0°C for about 10 min and then stirred at rt for about 72h. To mixture was added satured aqueous NH4Cl (25 mL) and water (10 mL). The aqueous layer was separated and extracted with DCM (2*50 mL). The combined organic layers were washed with brine (20 mL) dried over MgSO4, filtered and concentrated under reducced pressure. The residue was purified by column chromatography (80 g silica gel) eluting with 10 to 25 % EtOAc / Heptane to give 3-methyl-6-nitro-1-((2-(trimethylsilyl-ethoxy)methyl)-1H-indazole (1.915 g, 50%). 

Patent reference: WO2012048222 (Abbott)

Deprotection

In a vial, SEM protective compound (0.94 g, 0.19 mmol) and an aqueous of HCl (6N, 0.401 mL, 2.41 mmol) in DCE (4 mL) were added. The mixture was heated at about 70°C for about 15h. The mixture was concentrated under reduced pressure and 1,4-dioxane (4 mL) and NH4OH  (0.956 mL, 7.36 mmol) were added. The mixture wasz heated at about 75°C for about 3h, concentrated under reduced pressure and the residue was suspended in MeOH (1 mL) and filtered. The filtrate was purified by column chromatography eluting with 35 to 85% of 10% MeOH in DCM / DCM (12 g silica gel) to give deprotective compound (0.029g, 42%). 

Patent reference: WO2012048222 (Abbott)

 

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