Sodium Dithionite → tert-butyl 3-(5-methoxy-3-(3-methoxypropyl)-3H-imidazo[4,5-b]pyridin-2-yl)piperidine-1-carboxylate

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Reaction Steps

6-Methoxy-N-(3-methoxypropyl)-3-nitropyridin-2-amine (33B) (1.56 mmol max, crude oil) and (R)-tert-butyl 3-formylpiperidine-1-carboxylate (1.56 mmol, 0.332 g) were added to an oven dried 50 mL round-bottomed flask equipped with a reflux condenser and for stirring under nitrogen. Ethanol (4 mL) and dimethyl sulfoxide (2 mL) were added and the solution was allowed to stir at room temperature for 5 min. Sodium hydrosulfite (4.68 mmol; 0.959 g of 85%) was then added and the resultant mixture was heated to reflux and allowed to stir for 16 hr. The reaction solution was then concentrated in-vacuo, poured into water (100 mL), extracted with ethyl acetate, and washed once with saturated aqueous sodium chloride. The organic layer was collected and subsequently dried with anhydrous Na2SO4 and filtered. This filtrate was collected, concentrated, and dried in-vacuo affording a brown oil that was further purified by silica gel chromatography (20% CH3CN/CH2Cl2) to afford tert-butyl 3-(5-methoxy-3-(3-methoxypropyl)-3H-imidazo[4,5-b]pyridin-2-yl)piperidine-1-carboxylate (33C) as a clear oil (1.19 mmol, 0.481 g, 76% yield over 2-steps). 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.48 (s, 9H) 1.54-1.70 (m, 1H) 1.84 (dt, J=13.83, 2.81Hz, 1H) 2.02-2.21 (m, 4H) 2.73-2.88 (m, 1H) 2.96-3.18 (m, 2H) 3.29-3.41 (m, 5H) 3.98 (s, 3H) 4.08-4.44 (m, 4H) 6.65 (d, J=8.59 Hz, 1H) 7.86 (d, J=8.59 Hz, 1H). ESI-MS: m/z 405.5 (M+H)+.

Provenance & Evidence