Stereoselective reduction of methyl 3-oxo-2-trityloxyiminostearate

a-Diphenyl pyrrolidinemethanol (63 mg) was placed in a 25mL threenecked flask equipped with a magnetic stirrer bar, under nitrogen. A solution of trimethyl borate (31 mg) in dry tetrahydrofuran (5mL) was added. The mixture was stirred for 1 hour at room temperature. 

After being stirred for 2 hours at room temperature, 10 M borane-dimethyl-sulfide complex (2.0 mL) was added. The mixture was heated under reflux for 65 hours. The resulting mixture was cooled to room temperature and cautiously transferred into 2N hydrochloric acid (10 mL) in a 200 mL round-bottomed flask equipped with a magnetic stirrer bar using diethyl ether (10 mL). 

After being stirred for 1 hour at 60 °C, the mixture was cooled to room temperature and then made basic with sodium hydroxide (1.4 g). Benzoyl chloride (0.70 g) was added, and the mixture was stirred for 1 hour at room temperature and subsequently stirred for 2 hour at 60 °C with methanol (10 mL). 

The organic solvents were removed under reduced pressure using a rotary evaporator. The residue was transferred into a separating funnel with methylene chloride-tetrahydrofuran (2 1, 40 mL) and the phases were separated. The aqueous layer was extracted with methylene chloride-tetrahydrofuran (2 1, 2 x 40 mL). The combined organic layers were dried over magnesium sulfate, filtered and concentrated using a rotary evaporator. 

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The same procedure described for the stereoselective reduction of methyl 3-oxo-2-trityloxyiminostearate gave a white solid jV-benzoylsph ingamine (0.96 g, 94%) as a mixture of diastereomers. 

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