Isocyanate → (2S,5R)-1-benzyl-2,5-dimethyl-4-(tetrahydro-2H-pyran-4-yl)piperazine

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To a mixture of (2S,5R)-1-benzyl-2,5-dimethylpiperazine (11.0 g, 53.8 mmol) and of tetrahydro-4H-pyran-4-one (5.39 g, 53.8 mmol) at 0° C. was added Ti(IV) isopropoxide (19.2 mL, 67.3 mmol). The resulting mixture was stirred at rt overnight and an orange suspension was obtained. To the suspension was added EtOH (25 mL) and NaCNBH3 (4.27 g, 64.6 mmol, 1.20 eq). The resulting mixture was stirred at rt for 24 h. The reaction mixture was then quenched with water (5.0 mL) and a yellow solid was generated. The suspension was diluted with EtOAc (400 mL) and filtered. The filtrate was concentrated under reduced pressure. The residue was again diluted with EtOAc (500 mL), dried over Na2SO4, and filtered. The filtrate was collected and concentrated under reduced pressure to afford a yellow oil. The oil was diluted in THF (400 mL) and PS-isocyanate was added to remove secondary amine. The suspension was filtered and the filtrate concentrated. The residue was purified by column chromatography using 50:5:1 CHCl3/MeOH/Et3N to afford the desired compound as yellow oil (13.0 g, 84%)

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