5-(4-Fluorobenzyl)-4-(4-isobutoxybenzyl)-3-oxo-1-oxa-4,9-diaza-spiro[5.5]undecane-9-carboxylic acid benzyl ester → 5-(4-Fluorobenzyl)-4-(4-isobutoxybenzyl)-1-oxa-4,9-diaza-spiro[5.5]undecan-3-one

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Reaction Steps

The spirocycle 103NLS33 (62 mg, 0.107 mmol) in ethanol (5 mL) was N-CBz-deprotected by hydrogenation in presence of Pd/C (10%, 40 mg) under H2-balloon pressure. The catalyst was filtered off and the filtrate evaporated under reduced pressure to give crude 5-(4-fluorobenzyl)-4-(4-isobutoxybenzyl)-1-oxa-4,9-diaza-spiro[5.5]undecan-3-one. The residue was dissolved in methanol (3 mL), formaldehyde (37% in water, 0.017 mL) added, followed by the addition of acetic acid (0.03 mL) and sodium cyanoborohydride (60 mg, 0.95 mmol). The solution was stirred at rt for 5 h, then water was added and the mixture basified with 2 N aq. NaOH solution. The mixture was extracted three times with dichloromethane, the combined organic layers washed with sat. ammonium chloride solution and brine, dried over Na2SO4, filtered and evaporated to dryness. The residue was purified by column chromatography on silica gel, eluting with a stepwise gradient of 0–7% methanol in dichloromethane, giving 103NLS35B (43 mg, 88% over both steps) as a colorless oil. The compound was converted to its HCl form by treatment with 2 M HCl in diethylether as described above for 69NLS75, affording the salt as a colorless powder.

Provenance & Evidence