1,4-Dioxaspiro[4.5]decan-8-one → 9-(Phenylmethyl)-1,4-dioxa-9-azadispiro[4.2.4.2]tetradecane

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A solution of 669 mg (1.62 mmol) of 9-benzyl-11-iodo-1,4-dioxa-9-aza-dispiro[4.2.4.2]tetradecane (prepared starting from 1,4-dioxa-spiro[4.5]decan-8-one according to the procedure published in J. Bonjoch et al., Tetrahedron Lett. 2003, 44, 8387) in methanol (30 mL) was treated with 50 mg of 20% palladium hydroxide on activated carbon and the mixture was stirred overnight under a hydrogen atmosphere (1 atm) at room temperature. The catalyst was removed by filtration, and the filtrate was evaporated in vacuo to give crude 9-benzyl-1,4-dioxa-9-aza-dispiro[4.2.4.2]tetradecane, which was directly dissolved in a 1:1 mixture of acetone and 6N aqueous hydrochloric acid (10 mL) and stirred at room temperature. After the reaction went to completion, the mixture was poured onto a saturated aqueous sodium bicarbonate solution and extracted twice with ethyl acetate. The combined organics were washed with brine and water, dried over sodium sulphate, filtered and concentrated. Purification by flash chromatography (SiO2, 0%→100% ethylacetate in heptane) gave 180 mg (0.74 mmol) of 1-benzyl-1-aza-spiro[4.5]decan-8-one, which was dissolved in ethanol (10 mL) and cooled to 0° C. Then, sodium borohydride (14 mg, 0.37 mmol, 0.5 eq.) was added. The reaction mixture was slowly warmed to room temperature and stirred for 2 h before being concentrated and partitioned between dichloromethane and saturated aqueous sodium bicarbonate solution. The mixture was stirred vigorously for 15 min, before the phases were separated and the aqueous phase was extracted three times with dichloromethane and twice with a mixture of dichloromethane and 2-propanol (3:1). The combined organic phases were concentrated in vacuo to give crude trans-1-benzyl-1-aza-spiro[4.5]decan-8-ol. The alcohol was dissolved in ethanol (4 mL) containing acetic acid (15 μL) and was treated with 15 mg of palladium on charcoal (10%). The mixture was stirred under a hydrogen atmosphere (1 atm) until conversion was complete. The catalyst was filtered off and the reaction mixture was evaporated to dryness, then lyophilized from 1N HCl and water, successively, to give the crude title compound as its hydrochloride. Rt=0.17 min (Method 3). Detected mass: 156.2 (M+H+).

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