Cyclopentanone → alpha-Cyclopentylmandelic acid, (+)-

Beteiligte Stoffe

Reaktionsschritte

To a solution of 293 mg of (2S,5S)-2-(t-butyl)-5-phenyl-1,3-dioxolan-4-one, which had been synthesized following the method of D. Seebach, et al. [Tetrahedron, Vol. 40, pp. 1313-1324 (1984)], in 10 ml of tetrahydrofuran, 1.0 ml of a hexane solution of 1.5 M lithium diisopropylamide was added dropwise at -78° C., followed by 30 minutes' stirring, addition of 0.15 ml of cyclopentanone, 1 hour's stirring at the same temperature and then addition of a solution of 510 mg of N-phenyltrifluoromethanesulfonimide in 5 ml of tetrahydrofuran. The reaction mixture was stirred overnight while being restored to room temperature. The resultant reaction mixture was poured into saturated aqueous ammonium chloride solution and extracted with ethyl acetate. The extract was washed with saturated saline solution, dried over anhydrous magnesium sulfate and removed of the solvent by reduced pressure distillation. The residue was purified by silica gel column chromatography (hexane/ethyl acetate=40/1), and 361 mg of an yellow oily substance was obtained, 113 mg of which was dissolved in 4 ml of methanol. To the solution 45 mg of sodium acetate and 15 mg of 10% palladium-on-carbon were added and stirred for 6 hours in a hydrogen atmosphere at normal pressure and room temperature. The reaction mixture was filtered through celite pad and removed of the solvent by reduced pressure distillation. To the residue ethyl acetate and saturated aqueous sodium hydrogencarbonate solution were added. The organic layer was separated, washed with saturated saline solution, dried over anhydrous magnesium sulfate and removed of the solvent by reduced pressure distillation. The residue was purified by preparative thin layer chromatography (Kieselgel™ 60F254, Art 5744: Merck, hexane/ethyl acetate=19/1) to give 63 mg of a colorless oily substance. This product was dissolved in 1 ml of methanol, added with 1 ml of 1N sodium hydroxide solution and stirred for 3 hours at 60° C. Distilling the methanol off under reduced pressure, the remaining reaction mixture was washed with diethyl ether, made acidic with 1N hydrochloric acid and extracted with chloroform. The organic layer was washed with saturated saline solution, dried over anhydrous magnesium sulfate and removed of the solvent by reduced pressure distillation, to give 46 mg of the title compound as a white solid.

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