Hexamethyldisilazane → 2-[4-(1-Methylpiperidin-4-ylidene)-4,10-dihydro-9-oxa-3-thiabenzo[f]azulen-6-yl]propionic acid hydrochloride

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Hexamethyldisilazane (5.0 mL, 31.2 mmol) was ice-cooled in an argon atmosphere, and a 1.6 mol/L butyllithium-hexane solution (19.5 mL, 31.2 mmol) was added dropwise thereto. After stirring the mixture for 30 minutes, t-butyl propionate (2.1 g, 16.1 mmol) was added dropwise to the solution, and stirred for 30 minutes. Further, Pd(dba)2 (0.45 g, 0.8 mmol) and N,N′-(2,6-diisopropylphenyl)dihydroimidazolium chloride (0.34 g, 0.8 mmol) were added thereto, the mixture was stirred for 10 minutes, and a toluene (25 mL) solution of 4-(6-bromo-10H-9-oxa-3-thiabenzo[f]azulen-4-ylidene)-1-methylpiperidine (3.0 g, 8.0 mmol) was then added dropwise thereto. The mixture was stirred overnight at room temperature, water was then added to the reaction mixture, and the product was extracted with ethyl acetate. The solvents in the organic layer were distilled off under a reduced pressure, and the residue was purified by silica gel column chromatography (hexane-ethyl acetate). The purified compound was dissolved in dioxane (10 mL), a 4 mol/L hydrogen chloride-dioxane solution (12.5 mL, 50 mmol) was added to the solution, and the mixture was stirred overnight. The solvents were distilled off under a reduced pressure, and the precipitated crystals were collected by filtration, to give 1.5 g (69%) of the captioned compound.

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