[O:1]1[CH:5]=[CH:4][CH:3]=[C:2]1[C:6](=[N:10][OH:11])[C:7]([OH:9])=[O:8].CC(C)([O-])C.[K+].Br[C:19]([CH3:28])([CH3:27])[C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21].Cl>CS(C)=O>[C:23]([O:22][C:20]([C:19]([O:11][N:10]=[C:6]([C:2]1[O:1][CH:5]=[CH:4][CH:3]=1)[C:7]([OH:9])=[O:8])([CH3:28])[CH3:27])=[O:21])([CH3:26])([CH3:25])[CH3:24]A solution of 2-(fur-2-yl)-2-hydroxyiminoacetic acid (syn isomer) (14.1 g) in dimethyl sulphoxide (100 ml) was added all at once to a magnetically stirred solution of potassium t-butoxide (22.4 g) in dimethyl sulphoxide (400 ml), the reaction mixture being maintained under an atmosphere of dry nitrogen. A gel was formed which, on stirring, become a finely divided, yellow solid. Stirring was continued for one hour, and then a solution of t-butyl 2-bromo-2-methylpropionate (24.0 g) in dimethyl sulphoxide (50 ml) was added over one hour to the reaction mixture at room temperature. After addition was complete, the resulting solution was stirred for a further hour. The reaction was poured into ice-water (1.5 liters) and acidified under ether (500 ml) to pH 1.8 with concentrated hydrochloric acid. The two layers were separated, and the aqueous layer was extracted with more ether. The combined ether extracts were washed once with water, then extracted with aqueous sodium bicarbonate solution. The combined alkaline extracts were acidified under ether to pH 1.8 with concentrated hydrochloric acid, and the acid solution was extracted further with ether. The combined ether extracts were washed (water, saturated brine), dried, and concentrated to a yellow oil, which crystallised under high vacuum (22.41 g, 83%), λmax (EtOH) 272.5 nm (ε 15,400).
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