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Following the general procedure for the preparation of carboxylic esters from carboxylic acids of Description 15, (2R)-4-[(3-chloropropyl)sulfonyloxy]-3,3-dimethyl-2-(phenylmethoxy)butanoic acid (11) (1.1 g, 3.1 mmol) dissolved in 30 mL of anhydrous dichloromethane (DCM) was reacted with 1.8 mL (3.6 mmol) of oxalyl chloride (2.0 M in DCM). After completion of the reaction, a solution of (2-dimethylamino)ethanol (0.55 g, 6.2 mmol) and 0.50 mL of pyridine (0.49 g, 6.2 mmol) in 20 mL of anhydrous dichloromethane (DCM) was added to the acid chloride. After work-up, the crude material was purified by silica gel column chromatography using a mixture of ethyl acetate (EtOAc) and methanol (MeOH) as eluent (EtOAc/MeOH=9:1) to provide 0.7 g (50% yield) of the title compound (28a) as a colorless oil. Rf=0.23 (EtOAc/MeOH=9:1). 1H NMR (400 MHz, CDCl3): δ=1.08 (s, 3H), 1.09 (s, 3H), 2.28-2.30 (m, 8H), 2.57-2.60 (m, 2H), 3.22-3.26 (m, 2H), 3.64 (t, J=6.0 Hz, 2H), 3.88 (s, 1H), 4.02 (d, J=9.2 Hz, 1H), 4.21 (d, J=9.6 Hz, 1H), 4.27-4.32 (m, 1H), 4.32 (d, J=11.2 Hz, 1H), 4.65 (d, J=11.6 Hz, 1H), 7.30-7.35 (m, 5H) ppm. MS (ESI) m/z 450.04 (M+H)+. The analytical data is consistent with the proposed structure.

1. customAfter completion of the reaction
2. customAfter work-up, the crude material was purified by silica gel column chromatography
3. additiona mixture of ethyl acetate (EtOAc) and methanol (MeOH) as eluent (EtOAc/MeOH=9:1)