Methanol → 5-carboxymethyl-3-methyl-1H-pyrrole-2,4-dicarboxylic acid 2-tert-butyl ester 4-ethyl ester

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A solution of 5-ethoxycarbonylmethyl-3-methyl-1H-pyrrole-2,4-dicarboxylic acid 2-tert-butyl ester 4-ethyl ester (30 g, 88.5 mmol) in tetrahydrofuran (268 ml), and methanol (134 ml) was added with aqueous lithium hydroxide solution (0.465 mol lithium hydroxide in 197 ml of water). Upon completion of the addition, the mixture was stirred for 1.5 hours at room temperature. The resulting mixture was concentrated under reduced pressure. The residue was added with water (200 ml) and extracted with ethyl ether. The water phase was adjusted to pH 1˜3 with 20% hydrochloric acid solution. The resulting solid was filtered, washed with ethyl ether, and dried in vacuo to give 5-carboxymethyl-3-methyl-1H-pyrrole-2,4-dicarboxylic acid 2-tert-butyl ester 4-ethyl ester (20 g, 72.3%) as a yellow solid.

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