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 5\115 min of exposure to LIDA, almost exclusively at the 5- rather than the 4-position. Trappin

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化学文献翻译Iodinebeingtheleastacidifyingofallhalogens,protonabstractionfrom2,6-difluoro-3-iodopyridine(1)

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 5\115 min of exposure to LIDA, almost exclusively at the 5- rather than the 4-position. Trappin
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 5\115 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 acid (20; 98%) or (5-chloro-2,6-difluoropyridin-3-yl)trimethylsilane (21; 97%)respectively. Using iodine chloride, the acid 20 was iododesilylated to the 2,6-difluoro-5-iodopyridine-3-carboxylicacid (17; 96%). Under the same conditions, the chlorosilane 21 gave 3-chloro-2,6-difluoro-5-iodopyridine (15; 93%). The latter compound was converted into the 5-chloro-2,6-difluoropyridine-3-carboxylic acid (22; 91%), by halogen/metal permutation followed by carboxylation.
Condensation of the 5-lithiated (2,6-difluoropyridin-3-yl)trimethylsilane (5) with chlorotrimethylsilane provided the (2,6-difluoropyridin-3,5-diyl)bis(trimethylsilane) (23; 94%)
which reacted with iodine chloride smoothly under double iododesilylation to afford the 2,6-difluoro-3,5-diiodopyridine (18; 93%) whereas the bromodesilylation effected with elemental bromine rigorously stopped after a unilateral displacement producing (5-bromo-2,6-difluoropyridin-3-yl)trimethylsilane (24; 95%). 3,5-Dibromo-2,6-difluoro-pyridine (25; 90%) was found to be accessible only indirectly by subjecting 3-bromo-2,6-difluoro-5-iodopyridylsi-lane (26) to element-specific halogen/metal permutation and subsequent bromination. The latter precursor 26 was readily prepared by iododesilylation of the bromopyridyl-silane 24 in 91% yield
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碘作为至少所有卤素酸化，从2,6 -二氟- 3 - iodopyridine（1）发生初期，即在5质子抽象？15分钟接触利达，几乎完全在5 - 而不是4位。用干冰或碘俘获提供的2,6 -二氟- 5 - iodopyridine - 3 -羧酸（17; 72％）或2,6 -二氟- 3 ,5 - diiodopyridine（18; 81％）分别。然而，当与力达反应时间延长至30小时，可逆回到起始原料为1套在4位零星去质子化的阶段。这引发instan -脲嘧啶1碱度梯度驱动的重型halogenmigration生产的异构2,6 -二氟- 3 ,4 - diiodopyridine（19，80％碘化后）。
在力达促销去质子化的（2,6 - difluoropyridin - 3 -基）三甲基硅烷（5）也发生在5位的地方。中间被困干冰或1,1,2 -三氯- 1 ,2,2 -三氟给2,6 -二氟- 5 -（三甲基硅基）吡啶- 3 -羧酸（20; 98％）或（五氯-2,6 - difluoropyridin - 3 -基）三甲基硅烷（21; 97％）分别。使用氯化碘，酸是iododesilylated 20到2,6 -二氟- 5 - iodopyridine - 3 - carboxylicacid（17; 96％）。在相同条件下，氯21个国家给予3 -氯-2,6 -二氟- 5 - iodopyridine（15; 93％）。后者化合物转化为5 -氯- 2 ,6 -二氟- 3 -羧酸（22; 91％）的卤素/金属羧其次置换。
凝结的5 -锂（2,6 - difluoropyridin - 3基）三甲基硅烷和甲基氯硅烷（5）提供的（2,6 - difluoropyridin -3,5 - diyl）双（三甲基硅烷）（23; 94％）
其中反应下顺利双重iododesilylation负担2,6 -二氟- 3 ,5 - diiodopyridine（18; 93％，而与元素溴实施的bromodesilylation）严格生产后单方面位移（5溴-2停止与氯化碘， 6 difluoropyridin - 3 -基）三甲基硅烷（24，95％）。 3,5 -二溴-2,6二氟吡啶（25，90％）被发现是访问只是间接遭受3 -溴- 2 ,6 -二氟- 5 - iodopyridylsi线（26），以元素为具体的卤素/金属置换和随后的溴代。后者的前身是26容易由溴硅烷24 iododesilylation编制91％的收率

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