[Cl-:1].[Al+3].[Cl-].[Cl-].[CH3:5][O:6][C:7]1[C:12]([O:13][CH3:14])=[CH:11][CH:10]=[CH:9][C:8]=1[CH2:15][CH2:16][CH:17]1[C:21](=[O:22])OC(=O)[N:18]1[CH3:24].O.CC(C)=O>C(Cl)Cl>[ClH:1].[CH3:5][O:6][C:7]1[C:12]([O:13][CH3:14])=[CH:11][CH:10]=[C:9]2[C:8]=1[CH2:15][CH2:16][CH:17]([NH:18][CH3:24])[C:21]2=[O:22]12.5 g of anhydrous aluminium chloride (0.094 mole) in 200 ml of methylene chloride are placed into a 3 l round-bottomed flask, under nitrogen atmosphere, cooling to 0° C., then 12.5 g of 4-[2-(2,3-Dimethoxyphenyl)-ethyl]-N-methyl -2,5-oxazolidindione dissolved in 200 ml of methylene chloride are added in about 10 minutes, keeping T<10° C. The mixture is stirred for 30 minutes at T<10° C., then for 1 hour a room temperature. The mixture is cooled again at 0° C. and 200 ml of water are dropped therein, keeping T<20° C., then the mixture is stirred at room temperature for about 1 hour and the organic phase is separated and extracted with water (3×400 ml). The combined aqueous phases are slowly alkalinized with 400 ml of a 20% KHCO3 solution and extracted with 3×400 ml of chloroform. The organic phase is then dried over sodium sulphate, filtered, markedly acidified with methanolic HCl (1M) and evaporated to dryness to obtain a waxy compound, which is taken up into 150 ml of acetone a 50° C., stirred for one hour under stirring and left to stand overnight, then is filtered and dried under vacuum at room temperature. Yield: 8.2 g, 67% (moles); TLC: methylene chloride/methanol, 90/10; Rf=0.35; M.p.=208°-209° C.
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