Citric Acid → 3-{(2R)-2-[(3S,4R)-3-[(1R)-1-t-butyldimethylsilyloxyethyl]-2-oxoazetidin-4-yl)propionyl}-(3aS-cis)-3,3a,8,8a-tetrahydro-2H-indeno[1,2-d]oxazol-2-one

Participants

Reaction Conditions

Reaction Steps

Under a nitrogen atmosphere, 231 mg (1.0 mmol) of 3-propionyl-(3aS-cis)-3,3a,8,8a-tetrahydro-2H-indeno[1,2-d]oxazol-2-one was charged in a 30-ml three-necked flask to dissolve it in 2 ml of tetrahydrofuran. To the resulting solution, 2.75 ml (2.2 mmol) of a tetrahydrofuran solution (0.8M) of t-butylmagnesium chloride was slowly added dropwise at room temperature. After the resulting mixture was allowed to react for 20 minutes under the same conditions, the reaction mixture was cooled to 5° C. and added with 2 ml of a tetrahydrofuran solution of 287 mg (1.0 mmol) of (3R,4R)-4-acetoxy-3-[(R)-1-tert-butyldimethylsilyloxyethyl]azetidin-2-one at the same temperature. After stirring for 10 minutes, 10 ml of ethyl acetate was added to the reaction mixture, followed by the dropwise addition of 2 ml of a 10% aqueous solution of citric acid. After separation, the organic layer was washed with 2 ml of a saturated aqueous solution of sodium bicarbonate and 2 ml of a saturated aqueous solution of sodium cloride, dried over anhydrous magnesium sulfate and distilled to remove the solvent. The residue was purified by column chromatography, whereby 308 mg (0.67 mmol) of a condensation product was obtained (yield: 67%, β:α=95:5).

Provenance & Evidence