化学文献翻译

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化学文献翻译
Iodine being the least acidifying of all halogens, proton abstraction from 2,6-difluoro-3-iodopyridine (1) occurred initially, i.e. upon 5115 min of exposure to LIDA, almost exclusively at the 5- rather than the 4-position. Trapping with dry ice or iodine provided the 2,6-difluoro-5-iodopyridine-3-carboxylic acid (17; 72%) or the 2,6-difluoro-3,5-diiodopyridine (18; 81%) respectively. However, when the reaction time with LIDA was prolonged to 30 h, reversible return to the starting material 1 set the stage for a sporadic deprotonation at the 4-position. This unleashed instan-taneously a basicity gradient-driven heavy halogenmigration producing the isomeric 2,6-difluoro-3,4-diiodopyridine (19; 80%) after iodination.
The LIDA-promoted deprotonation of (2,6-difluoropyridin-3-yl)trimethylsilane (5) also took place at the 5-position. The intermediate was trapped with dry ice or 1,1,2-trichloro-1,2,2-trifluoroethane to give 2,6-difluoro-5-(trimethylsilyl)pyridine-3-carboxylic

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