Methyl morpholine oxide → 2-{2-[6-(2-Carboxyethyl)-7-chloro-3-(3,5-dimethylphenyl)-2-oxo-1,2-dihydroquinolin-4-yloxy]-ethyl}-piperidine-1-carboxylic acid tert-butyl ester

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To a solution of 2-{2-[7-chloro-3-(3,5-dimethylphenyl)-6-(3-hydroxy-propyl)-2-oxo-1,2-dihydroquinolin-4-yloxy]-ethyl}-piperidine-1-carboxylic acid tert-butyl ester (176 mg in 3.0 mL methylene chloride) was added 20 mg powdered 4Å sieves, 73 mg of 4-methylmorpholine-N-oxide, followed by 11 mg tetrapropylammonium perruthenate(VII) and the mixture stirred at room temperature. After 3 hours, the solvent was removed in vacuo and the crude aldehyde product resolvated in a mixture of tert-butanol (2 mL) and sodium phosphate (1 mL of a 1.25M solution). To this was added 1.86 mL of a 1M aqueous solution of potassium permanganate. After 30 minutes, the mixture was extracted with ethyl acetate, dried over sodium sulfate and purified by flash chromatography on silica gel (hexane:ethyl acetate, 1:1; then methylene chloride:methanol, 90:10) to give the title compound (107 mg).

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