Sodium hydride → 6-bromo-2-methyl-1-(2-trimethylsilanylethoxymethyl)-1H-imidazo[4,5-b]pyridine

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Reaction Conditions

Reaction Steps

To 5.06 g of 5-bromo-2,3-diaminopyridine 46 (Ryabukhin et al (2006) Synthesis 21:3715-3726; Oguchi et al (2000) J. Med. Chem. 43(16):3052-3066; Seki et al (1995) J. Hetero. Chem. 32(3):1071-73; Fray et al (1995) J. Med. Chem. 38(18):3524-35) was added 50 mL acetic acid under N2 and the reaction was heated to reflux overnight. Complete reaction was confirmed by LCMS. The solution was concentrated in vacuo and purified by flash chromatography (DCM/MeOH) to give 4.68 g of 6-bromo-2-methyl-3H-imidazo[4,5-b]pyridine 51 (82% yield), which may also be prepared by the methods of Cee et al (2007) J. Med. Chem. 50(4):627-40; Itoh et al (1982) J. Hetero. Chem. 19(3):513-17. 6-Bromo-2-methyl-3H-imidazo[4,5-b]pyridine (4.68 g) in 150 mL THF was added to 0.63 g (1.1 eq) NaH in 10 mL THF under N2 at −78° C. The reaction was stirred at −78° C. for 30 minutes followed by the addition of 3.86 g of SEM-Cl (1.05 eq) and allowed to warm up to room temperature. The reaction was stirred at room temperature 4.5 hours and complete reaction was confirmed by LCMS. The reaction was quenched with water followed by the addition of NaCl (not saturated) and the two products extracted with EtOAc and concentrated in vacuo. The two regioisomers were separated by flash chromatography (EtOAc/Hexanes) to give 2.84 g 6-bromo-2-methyl-3-((2-(trimethylsilyl)ethoxy)methyl)-3H-imidazo[4,5-b]pyridine 52 and 1.94 g 6-bromo-2-methyl-1-((2-(trimethylsilyl)ethoxy)methyl)-1H-imidazo[4,5-b]pyridine 53 (63% overall yield). 6-Bromo-2-methyl-3-((2-(trimethylsilyl)ethoxy)methyl)-3H-imidazo[4,5-b]pyridine 52 (2.08 g) was dissolved in 50 mL toluene followed by the addition of 2.32 g (1.5 eq) of bis(pinacolato)diboron, 0.24 g (0.05 eq) of PdCl2(dppf), and 1.79 g (3.0 eq) of KOAc. The reaction mixture was heated to 95° C. under N2 and let stir overnight. Complete reaction confirmed by LCMS. The mixture was cooled to room temperature, rotovapped and purified by flash chromatography (EtOAc/Hexanes) to give 1.83 g of 2-methyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-3-((2-(trimethylsilyl)ethoxy)methyl)-3H-imidazo[4,5-b]pyridine 54 (77% yield). MS (Q1) 390.2 (M)+

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