[O-]S(C(F)(F)F)(=O)=O.C([B+]CCCC)CCC.[F:18][CH:19]([C:24]([F:27])([F:26])[F:25])[C:20]([O:22][CH3:23])=[O:21].C(N(C(C)C)CC)(C)C.[CH:37](=[O:39])[CH3:38]>ClCCl>[F:18][C:19]([C:24]([F:27])([F:26])[F:25])([CH:37]([OH:39])[CH3:38])[C:20]([O:22][CH3:23])=[O:21]Dibutylboron triflate (5 g) was added to a stirred solution of methyl 2,3,3,3-tetrafluoropropionate (2.9 g) in dichloromethane at 0° C. under nitrogen. After 15 minutes, the solution was cooled to -10° C. and diisopropylethylamine (3.8 ml) was added in portions. After 30 minutes, freshly distilled acetaldehyde (2 ml) was added in small portions, keeping the temperature at -10° C. The reaction was stirred at -10° C. for 1 hour before quenching with a mixture of pH7 phosphate buffer (60 ml), aqueous hydrogen peroxide (100 vol; 15 ml) and crushed ice and stirring for 1.5 hours. The organic phase was separated and the aqueous layer further extracted with dichloromethane. The combined organic phases were washed with aquesous sodium metabisulphite and with brine, dried (MgSO4) and concentrated under reduced pressure to give a pink oil (2.2 g) which was distilled using a Kugelrohr apparatus. The fraction distilling at 40° C. (air bath temperature) and at 0.05 mmHg was collected; 1H NMR (270 MHz; CDCl3) (signals recorded for a 50:50 mixture of diastereomers) δ 1.34 (1.5H,d), 1.42 (1.5H,d), 2.2(1H,bs), 3.91(1.5H,bs), 3.94(1.5H,s), 4.35-4.52(1H,m) ppm.
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