Diisopropylethylamine → 1-(4-ethynylbenzyl)-3,5-dimethyl-1H-pyrazol-4-yl-acetic acid tert.-butyl ester

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Reaction Steps

To a stirred solution of 1-(4-iodobenzyl)-3,5-dimethyl-1H-pyrazol-4-yl-acetic acid tert.-butyl ester (12.2 g) in tetrahydrofuran (100 ml) at room temperature is added diisopropylethylamine (12.3 ml). The solution is degassed and put under argon. Ethynyltrimethylsilane (4.5 ml), copper(I)iodide (543 mg) and bis-(triphenylphosphine)-palladiumdichloride (1.0 g) are added. After 15 h of stirring, the reaction is absorbed onto Extrelute and purified by flash chromatography (4:1 isocratic-cyclohexane:ethyl acetate) to yield a solid (10.7 g; [M+H]=397; HPLC retention time 1.71 min (Method J)). The solid is dissolved in tetrahydrofuran (200 ml) and is stirred together with tetrabutylammonium fluoride (1 M in THF, 28 ml). After 15 h at room temperature, the reaction mixture is concentrated in vacuo. The residue is purified by flash chromatography (4:1 isocratic-cyclohexane:ethyl acetate) to yield 1-(4-ethynylbenzyl)-3,5-dimethyl-1H-pyrazol-4-yl-acetic acid tert.-butyl ester (6.8 g; [M+H]=325; HPLC retention time 1.47 min (Method J)).

Provenance & Evidence