[CH2:1]([C:5]1[C:10]([O:11][CH3:12])=[C:9]([CH3:13])[C:8]([CH3:14])=[C:7]([O:15][CH3:16])[C:6]=1[CH3:17])[CH2:2][C:3]#[CH:4].C([Li])CCC.Cl[C:24]([O:26][CH3:27])=[O:25].[Cl-].[NH4+]>C1COCC1>[CH3:12][O:11][C:10]1[C:9]([CH3:13])=[C:8]([CH3:14])[C:7]([O:15][CH3:16])=[C:6]([CH3:17])[C:5]=1[CH2:1][CH2:2][C:3]#[C:4][C:24]([O:26][CH3:27])=[O:25]A solution of 5 g (21.5 mmol) of 1-(3-butynyl)-3,6-dimethoxy-2,4,5-trimethylbenzene in 80 ml of THF was cooled to -78° C. and treated firstly with 13.4 ml of a 1.6M n-butyllithium solution and then with 2.2 g (23.3 mmol) of methyl chloroformate. The mixture was left at -78° C. for 1 hour, then warmed to -20° C., held at this temperature for 2 hours and finally poured into saturated ammonium chloride solution. Extraction with ethyl acetate yielded, after washing the extracts with water and drying over sodium sulphate, a yellow oil which was purified on silica gel (eluent: hexane/ethyl acetate 95:5→90:10). There were obtained 3.6 g of spontaneously crystallizing methyl 5-(2,5-dimethoxy-3,4,6-trimethylphenyl)-2-pentynoate. M.P. 71°-72° C.
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