Benzyl 4-formylpiperidine-1-carboxylate → 4-[(R)-[[(R)-(1,1-Dimethylethyl)sulfinyl]amino]phenylmethyl]-1-piperidinecarboxylic acid, phenylmethyl ester

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A mixture of 4-formyl-piperidine-1-carboxylic acid, benzyl ester (0.96 g), (R)-2-methyl-2-propanesulfinamide (0.51 g), anhydrous copper(II) sulphate (1.5 g) and dichloromethane (20 mL) was stirred at room temperature for 48 h. Copper(II) sulphate was filtered off and the filtrate concentrated. The residue was treated with dry dichloromethane (15 mL) and cooled to −78° C. A solution of phenylmagnesium bromide in diethyl ether (3M, 4 mL) was added dropwise. The mixture was slowly warmed to 0° C., then quenched with sat. aqueous NH4Cl solution. The mixture was stirred for 15 min and extracted into dichloromethane. The organic phase was dried (Na2SO4), filtered and concentrated in vacuo. The residue was purified (SiO2 chromatography eluting with iso-hexane:ethyl acetate (0-100%)) to give the title compound (623 mg).

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