The general procedure for the synthesis of methyl 2-(2-hydroxy-4,5-dimethoxybenzoylamino)thiazole-4-carboxylate from methyl 2-aminothiazole-4-carboxylate and 2-hydroxy-4,5-dimethoxybenzoic acid was as follows: 39.8 g (0.2 mol) 2-hydroxy-4,5-dimethoxybenzoic acid, 38 g (0.24 mol) 2-aminothiazole-4-carboxylate and 89.9 g (0.3 mol) 4,6-diphenoxy-2-chloro-1,3,5-triazine were suspended in a solution containing 800 mL of tetrahydrogen tetraoxide. methyl ester and 89.9 g (0.3 mol) 4,6-diphenoxy-2-chloro-1,3,5-triazine were suspended in a reaction flask containing 800 mL of tetrahydrofuran. A mixed solution consisting of 50.6 g (0.5 mol) N-methylmorpholine and 200 mL of tetrahydrofuran was added dropwise under stirring in an ice water bath. The dropwise addition was controlled to be completed within 20 min, after which stirring was continued for 1 h. The mixture was subsequently stirred for 2 h at room temperature. Stirring was stopped, the reaction solution was poured into water for pulping, crystallized in an ice bath, filtered and dried in vacuum to afford 65.1 g of methyl 2-(2-hydroxy-4,5-dimethoxybenzoylamino)thiazole-4-carboxylate as a white solid in 96.2% yield and 99.8% purity by HPLC.
