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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 dichloromethane 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-methylpropanol (0.57 mL, 0.46 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 hexane (Hxn) as eluent (EtOAc/Hxn=1:5) to provide 0.62 g (48% yield) of the title compound (30a) as a colorless oil. Rf=0.69 (EtOAc/Hxn=1:2). 1H NMR (400 MHz, CDCl3): δ=0.98 (d, J=6.4 Hz, 1H), 1.07 (s, 3H), 1.09 (s, 3H), 1.99 (septet, J=6.4 Hz, 1H), 2.25-2.34 (m, 2H), 3.22-3.26 (m, 2H), 3.64 (t, J=6.0 Hz, 2H), 3.86 (s, 1H), 3.89-4.01 (m, 3H), 4.23-4.25 (m, 1H), 4.35 (d, J=11.2 Hz, 1H), 4.64 (d, J=11.2 Hz, 1H), 7.29-7.39 (m, 5H) ppm. MS (ESI) m/z 435.16 (M+H)+, 457.11 (M+Na)+. The analytical data was 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 hexane (Hxn) as eluent (EtOAc/Hxn=1:5)