Cesium carbonate → 1,1-Dimethylethyl 1-(2,6-dimethyl-3-pyridinyl)-3-methyl-2-oxo-4-imidazolidinecarboxylate

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Reaction Steps

A solution of 1,1-dimethylethyl 3-methyl-2-oxo-4-imidazolidinecarboxylate (600 mg, 3.00 mmol) (prepared as described in step (iii) of Example 13, starting from (4S)-2-oxo-3-{[(phenylmethyl)oxy]carbonyl}-4-imidazolidinecarboxylic acid) and 3-bromo-2,6-dimethylpyridine (557 mg, 3.00 mmol) in 1,4-dioxane (20 ml) was treated with cesium carbonate (1464 mg, 4.49 mmol), Xantphos™ (130 mg, 0.225 mmol) and tris(dibenzylideneacetone)dipalladium(0) (68.6 mg, 0.075 mmol) and the mixture was heated at reflux under argon for 3 hours. After cooling to room temperature, the reaction mixture was diluted with water and extracted with ethyl acetate. The organic layers were combined, washed with water and brine and evaporated in vacuo. The residue was purified by silica gel chromatography eluting with 0-10% methanol in dichloromethane. The residue was dissolved in methanol and applied to a SCX ion exchange cartridge and washed with methanol and then 2M ammonia in methanol. The basic fractions were combined and evaporated to give 1,1-dimethylethyl 1-(2,6-dimethyl-3-pyridinyl)-3-methyl-2-oxo-4-imidazolidinecarboxylate (493 mg, 54%). LC/MS [M+H]+=306. (ii) A solution of 1,1-dimethylethyl 1-(2,6-dimethyl-3-pyridinyl)-3-methyl-2-oxo-4-imidazolidinecarboxylate (0.489 g, 1.6 mmol) in TFA/DCM (1:2, 9 ml) was stirred at room temperature for 16 hours. The solution was evaporated and the residue was co-evaporated with toluene and dried to give crude 1-(2,6-dimethyl-3-pyridinyl)-3-methyl-2-oxo-4-imidazolidinecarboxylic acid TFA salt, (assume ˜1.6 mmol) which was used in the next step. LC/MS [M+H]+=250.

Provenance & Evidence