C(Cl)(=O)C(Cl)=O.[CH3:7][O:8][C:9]1[CH:18]=[CH:17][C:16]2[C:11](=[CH:12][CH:13]=[CH:14][CH:15]=2)[C:10]=1[CH2:19][CH2:20][C:21]([OH:23])=O.[Cl-].[Al+3].[Cl-].[Cl-]>ClCCl.CN(C)C=O>[CH3:7][O:8][C:9]1[CH:18]=[CH:17][C:16]2[C:11]3[C:10]=1[CH2:19][CH2:20][C:21](=[O:23])[C:12]=3[CH:13]=[CH:14][CH:15]=2In a 250 ml three-necked flask, oxalyl chloride (1.95 ml, 2.19.10−2 mol, 1 eq.) is added dropwise, under argon, to a solution of the acid obtained in Step D (5 g, 2.17.10−2 mol) in anhydrous dichloromethane (225 ml) at 0° C. A few drops of anhydrous dimethylformamide are then added. After 1 hour at 0° C., slight evolution of gas is still observed and the three-necked flask is left at ambient temperature for 40 minutes. After return to 0° C., aluminium chloride (7.5 g, 5.62.10−2 mol, 2.6 eq.) is added using a spatula. The initially yellow solution becomes red, orange and then khaki-green. After 15 minutes' stirring at 0° C., the mixture is poured into an ice/1N HCl mixture. After separation of the phases and washings of the acidic aqueous phase with dichloromethane, the combined organic phases are washed with water, then treated with a saturated NaHCO3 solution and finally washed with a saturated NaCl solution. After drying over MgSO4 and evaporation under reduced pressure, the yellow oil obtained crystallises in a freezer.
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