Hydrochloric Acid → ((S)-4-hydroxy-4,5,6,7-tetrahydro-indazol-1-yl)-acetic acid ethyl ester

Participants

Reaction Steps

To a stirred solution of (4-oxo-4,5,6,7-tetrahydro-indazol-1-yl)-acetic acid ethyl ester (16.7 g, 75.0 mmol) in formic acid-triethylamine azeotropes (molar fraction of triethylamine: 0.2857, 45 mL) was added chloro-[(1S,2S)-N-(p-tolunenesulfonyl)-1,2-diphenylethanediamine](mesitylene)ruthenium(II) (1.86 g, 3.0 mmol). The reaction mixture was stirred at room temperature for 3 hours and then at 45° C. for 2.5 hours with occasional venting. After cooling to room temperature, 1N hydrochloric acid (50 mL) was added, followed by extraction with ethyl acetate (200 mL×3). The organic layers were combined, washed with brine (300 mL), dried over sodium sulfate, filtered and concentrated in vacuo. The residue was purified by column chromatography (gradient elution, 0-4% methanol in dichloromethane) to afford ((S)-4-hydroxy-4,5,6,7-tetrahydro-indazol-1-yl)-acetic acid ethyl ester (14.3 g, 85%) as a white solid with enantiomerical purity ≧99% as determined by Chiralpak™ IA column (condition: gradient: 50% hexane in ethanol, flow rate: 15 mL/min and retention time: 5.8 min for A enantiomer and 8.1 min for B enantiomer).

Provenance & Evidence