B(F)(F)F.CCOCC.[F:10][C:11]([F:30])([F:29])[C:12]1[CH:28]=[CH:27][C:15]([O:16][CH2:17][C:18]([O:20][CH2:21][C:22]2([CH3:26])[CH2:25][O:24][CH2:23]2)=[O:19])=[CH:14][CH:13]=1>ClCCl>[CH3:23][C:22]12[CH2:25][O:24][C:18]([CH2:17][O:16][C:15]3[CH:27]=[CH:28][C:12]([C:11]([F:30])([F:29])[F:10])=[CH:13][CH:14]=3)([O:19][CH2:26]1)[O:20][CH2:21]2Boron trifluoride diethyl etherate (1.48 ml) was added to a solution of the product from step (ii) (14.2 g) in dichloromethane at −78° C. The cooling bath was removed, the mixture, stirred for 3 h then triethylamine (6.2 ml) added. The mixture was reduced to half the volume under reduced pressure then filtered. The filtrate was evaporated under reduced pressure then the residue purified by chromatography on silica (pre-eluted with one column volume of neat triethylamine) eluting with dichloromethane, yield 11.1 g.
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