[H-].[Na+].[C:3](#[N:7])[CH2:4][C:5]#[N:6].Br[C:9]([CH3:15])([CH3:14])[C:10]([O:12][CH3:13])=[O:11].C(=O)([O-])O.[Na+]>C1COCC1>[C:5]([CH:4]([C:3]#[N:7])[C:9]([CH3:15])([CH3:14])[C:10]([O:12][CH3:13])=[O:11])#[N:6]In THF (91 ml), 1.816 g (45.411 mmol) of sodium hydride (60% in mineral oil) were admixed gradually with 3 g (45.411 mmol) of malononitrile. Subsequently, 5.876 ml (45.411 mmol) of methyl 2-bromo-2-methylpropanoate were added and the reaction mixture was stirred at room temperature overnight. Thereafter, another 5.876 ml (45.411 mmol) of methyl 2-bromo-2-methylpropanoate were added and the reaction mixture was heated to 50° C. overnight. Then yet another 1.762 ml (13.623 mmol) of methyl 2-bromo-2-methylpropanoate were added and the reaction mixture was heated to 50° C. for a further 4 h. The mixture was then admixed with saturated aqueous sodium hydrogencarbonate solution and extracted three times with ethyl acetate. The combined organic phases were washed with saturated aqueous sodium chloride solution, dried over sodium sulphate, filtered and concentrated to dryness. This gave 8.9 g of crude product, which was purified by chromatography on silica gel (4:1 cyclohexane-ethyl acetate).
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