Toluene → 2-[(Tert-butyl-dimethyl-silanyloxy)-cyclohexyl-methyl]-4-(2-chloro-ethyl)-3-methylene-5-oxo-pyrrolidine-2-carboxylic acid methyl ester

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Lithium diisopropylamide solution (0.67 M solution in tetrahydrofuran, 0.09 ml, 0.06 mmol, 1.0 equiv) was added dropwise via syringe to a stirred solution of 2-[(tert-butyl-dimethyl-silanyloxy)-cyclohexyl-methyl]-3-methyl-5-oxo-2,5-dihydro-1H-pyrrole-2-carboxylic acid methyl ester (23 mg, 0.06 mmol, 1.0 equiv) in tetrahydrofuran (1.5 ml) at −78° C. The reaction mixture was stirred at −78° C. for 30 min. Chlorotrimethylsilane (8 μl, 6.8 mg, 0.06 mmol, 1.0 equiv) was added and the resultant solution was stirred at −78° C. for 2.5 h. Another equiv of lithium diisopropylamide solution (0.67 M solution in tetrahydrofuran, 0.09 ml, 0.06 mmol, 1.0 equiv) was added dropwise at −78° C. The reaction mixture was stirred −78° C. for 30 min. A stock solution of trifluoro-methanesulfonic acid 2-chloro-ethyl ester in toluene (2.45 M, 0.1 ml, 0.24 mmol, 4.0 equiv) was added dropwise via syringe at −78° C. The reaction mixture was stirred at −78° C. for 50 min. A buffer solution (pH=7, 5 ml) was added at −78° C. The organic layer was separated, washed with brine solution (5 ml), dried over sodium sulfate and the solids were filtered. The filtrate was concentrated. The residue was purified by flash column chromatography (10% ethyl acetate-hexanes initially, grading to 20% ethyl acetate-hexanes) to furnish 2-[(tert-butyl-dimethyl-silanyloxy)-cyclohexyl-methyl]-4-(2-chloro-ethyl)-3-methylene-5-oxo-pyrrolidine-2-carboxylic acid methyl ester (16 mg, 59%) along with recovered starting material (5 mg, 22%).

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