[Cl:1][C:2]1[CH:9]=[C:6]([CH:7]=O)[C:5]([OH:10])=[C:4]([CH:11]=[O:12])[CH:3]=1.CS(C)=O.[F:17][C:18]([F:27])([F:26])/[CH:19]=[CH:20]/[C:21]([O:23][CH2:24][CH3:25])=[O:22].C(N(CC)CC)C>C(OCC)C.CCCCCC.C(OCC)(=O)C>[Cl:1][C:2]1[CH:3]=[C:4]([CH:11]=[O:12])[C:5]2[O:10][CH:19]([C:18]([F:17])([F:27])[F:26])[C:20]([C:21]([O:23][CH2:24][CH3:25])=[O:22])=[CH:7][C:6]=2[CH:9]=1
A stirred solution of the dialdehyde (Step 2)(1.13 g, 6.14 mmol), dimethyl sulfoxide (6 mL), ethyl 4,4,4-trifluorocrotonate (1.37 mL, 1.55 g, 9.21 mmoL) and triethylamine (1.71 mL, 1.24 g, 12.28 mmol) in a round bottom flask fitted with condenser was heated to 80° C. for 8 h. Upon cooling to room temperature the reaction was diluted with diethyl ether (100 mL) and the resulting mixture washed with aqueous sodium bicarbonate solution (3×75 mL), 1 N HCl solution (3×70 mL), and brine (1×75 mL), dried over MgSO4, filtered and concentrated in vacuo yielding a tan powder. This powder was taken up in hot hexane-ethyl acetate and filtered to remove insoluble matter. Upon cooling of the filtrate, crystallization followed by vacuum filtration yielded the desired ester as tan crystals (0.726 g, 35%): mp 118.1–119.7° C. This material was of suitable purity to use without further purification.
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