A solution of n-butyllithium in hexane (1.6 m, 19.6 ml, 31.4 mmol) was slowly added dropwise to a solution of (4-bromo-3-methoxyphenoxy)triisopropylsilane (8.67 g, 24.1 mmol) in THF (100 ml) at −15° C. After 15 min, a solution of 5-chloroisatin sodium salt [prepared by treating a solution of 5-chloroisatin (3.65 g, 20.1 mmol) in THF with one equivalent of sodium hydride at 0° C. for one h] was added dropwise to the solution of the organolithium species. The reaction mixture was allowed to warm to room temperature and was stirred for a further hour. Aqueous ammonium chloride solution was added to the reaction solution while stirring, and the mixture was extracted with ethyl acetate. The combined organic phase was washed with water and saturated sodium chloride solution, dried over magnesium sulfate and concentrated under reduced pressure. Purification by chromatography on silica gel (mobile phase 10-30% gradient of ethyl acetate in dichloromethane) afforded 3.8 g (41%) of the desired adduct.
