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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) (0.73 g, 1.9 mmol) dissolved in 20 mL of anhydrous dichloromethane (DCM) was reacted with 1.1 mL (2.2 mmol) of oxalyl chloride (2.0 M in DCM). After the reaction was completed, a solution of 2 mL (1.58 g, 49.4 mmol) of methanol (MeOH) and 0.16 mL of pyridine (0.15 g, 1.9 mmol) in 10 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 hexane (Hxn) (EtOAc/Hxn=1:2) as eluent to provide 0.62 g (83% yield) of the title compound (24a) as a colorless oil. Rf=0.59 (EtOAc/Hxn=1:2). 1H NMR (400 MHz, CDCl3): δ=1.06 (s, 3H), 1.07 (s, 3H), 2.25-2.32 (m, 2H), 3.22-3.26 (m, 2H), 3.65 (t, J=6.0 Hz, 2H), 3.77 (s, 3H), 3.87 (s, 1H), 3.98 (d, J=9.2 Hz, 1H), 4.21 (d, J=9.6 Hz, 1H), 4.36 (d, J=11.2 Hz, 1H), 4.63 (d, J=11.2 Hz, 1H), 7.32-7.36 (m, 5H) ppm. MS (ESI) m/z 392.90 (M+H)+, 414.91 (M+Na)+. The analytical data was consistent with the proposed structure.

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