[CH3:1][O:2][C:3](=[O:13])[CH:4]([C:9](=[O:12])[CH2:10][CH3:11])[C:5](=[O:8])[CH2:6][CH3:7].[C:14](=O)([O-])[O-].[Cs+].[Cs+].FC(F)(F)S(OC)(=O)=O>CC#N>[CH3:1][O:2][C:3](=[O:13])[C:4]([C:5](=[O:8])[CH2:6][CH3:7])=[C:9]([O:12][CH3:14])[CH2:10][CH3:11]7.50 g (40.3 mmol) of 3-oxo-2-propionyl-pentanoic acid methyl ester were dissolved in 40 ml of MeCN and the mixture cooled to 2° C. While stirring, 13.26 g (40.3 mmol) of caesium carbonate were added in small portions and the reaction then warmed up to RT. 6.86 g=4.73 ml (40.3 mmol) of methyl trifluoromethanesulfonate were then added drop by drop between 22 and 25° C. After 90 min, the reaction mixture was poured into crashed ice and extracted twice with Et2O; the organic phases were washed with water, dried over magnesium sulfate, filtered and evaporated to give 7.86 g of crude compound as yellow oil.
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