N1C2C(=CC(O[CH:12]([CH2:22][CH3:23])[C:13]([NH:15][C:16]([CH3:21])([CH3:20])[C:17]#[C:18][CH3:19])=[O:14])=CC=2)C=CC=1.[Br:24]C(CC)C(Br)=O.C(N(CC)CC)C.O>ClCCl>[Br:24][CH:12]([CH2:22][CH3:23])[C:13]([NH:15][C:16]([CH3:21])([CH3:20])[C:17]#[C:18][CH3:19])=[O:14]The product from Step 3 (5.0 g) was dissolved in dry dichloromethane (200 ml), cooled to 3° C. with stirring then 2-bromobutyryl bromide (6.25 g) was added followed by dropwise addition of dry triethylamine (10.93 ml), maintaining the reaction at 5° C. The suspension, which had formed during the reaction, was stirred at ambient temperature for 1 hour then water was added. The organic phase was separated, washed with water, dried over magnesium sulphate then evaporated under reduced pressure. The residue was fractionated by chromatography (silica; hexane/diethyl ether, 3:1 by volume) to give the required product, 5.2 g, as a colourless solid, m.p. 79–81° C.
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