[O:1]1[CH:6]=[C:5]([C:7]([OH:9])=[O:8])[CH2:4][CH2:3][CH2:2]1.[CH2:10](Br)[C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1.C([O-])([O-])=O.[K+].[K+]>CO.C(#N)C.[Pd]>[O:1]1[CH2:2][CH2:3][CH2:4][C@H:5]([C:7]([O:9][CH2:10][C:11]2[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=2)=[O:8])[CH2:6]1
Pd/C (10%, 3 g) was added to a solution of 3,4-dihydro-2H-pyran-5-carboxylic acid (7.0 g, 55 mmol) in MeOH (100 mL). The suspension was stirred under hydrogen atmosphere (100 psi) at 40° C. for 10 h. The catalyst was filtered off and washed with MeOH (50 mL). The filtrate and washings were combined and concentrated to dryness to afford crude product. The crude product was dissolved in acetonitrile (200 mL) and benzyl bromide (9.9 g, 58 mmol) and K2CO3 (19.0 g, 138 mmol) were added. The resulting suspension was heated at 50-60° C. for 4 h and then cooled to ambient temperature. The mixture was filtered and the filtration cake was washed with acetonitrile (50 mL). The filtrate and washings were combined and concentrated to dryness. The residue was purified by flash column chromatography on silica gel (Hexane/EtOAc=20:1) to afford a mixture (7.1 g) of (S)-benzyl tetrahydro-2H-pyran-3-carboxylate and (R)-benzyl tetrahydro-2H-pyran-3-carboxylate, which was separated by chiral prep-HPLC to afford (S)-benzyl tetrahydro-2H-pyran-3-carboxylate (2.1 g, 17% yield) and (R)-benzyl tetrahydro-2H-pyran-3-carboxylate (2.0 g, 16% yield), respectively.
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