During attempts to prepare functionalized 5-iodopyridine derivatives the unexpected formation of iodo[1,3]dioxolo[4,5-c]pyridines was discovered. The conversion of 3-alkoxypyridin-4-ols into the corresponding 5-iodo compounds was achieved by reaction with one equivalent of iodine or tetramethylammonium dichloroiodate under basic conditions. When three equivalents of iodine were used in chlorinated solvents, after 5-iodination, subsequent reaction of the 3-alkoxy group took place to form a 1,3-dioxolane ring with the 4-hydroxyl group. Generation of the resulting iodo[1,3]dioxolo[4,5-c]pyridines is explained by a radical process known as the Hofmann–Loffler–Freytag reaction. Two 6-ethynylpyridine derivatives were examined in the iodination process to establish a route to pyridine-containing macrocycles. The pentasubstituted 5-iodopyridine derivative 21 could be prepared; however, attempts to achieve cyclotrimerization of this building block under different conditions were not successful. Reaction of 21 with copper chloride allowed isolation of a copper acetylide 22, which aggregates to a triangular trimeric complex containing four copper(I) ions such as [23·Cu]+ as monitored by ESI mass spectrometry.

中文翻译：

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通过 Hofmann-Löffler-Freytag 反应意外一步形成 Iodo[1,3]dioxolo[4,5-c] 吡啶衍生物：含吡啶大环化合物的合成研究

在尝试制备功能化的 5-碘吡啶衍生物的过程中，意外地发现了碘[1,3] 二氧代 [4,5-c] 吡啶的形成。3-烷氧基吡啶-4-醇转化为相应的5-碘化合物是通过与一当量的碘或二氯碘酸四甲基铵在碱性条件下反应来实现的。当在氯化溶剂中使用三当量的碘时，5-碘化后，3-烷氧基发生后续反应，与 4-羟基形成 1,3-二氧戊环。生成的碘[1,3]二氧代[4,5-c]吡啶可以通过称为Hofmann-Loffler-Freytag反应的自由基过程来解释。在碘化过程中检查了两种 6-乙炔基吡啶衍生物，以建立含吡啶大环的途径。可制备五取代的5-碘吡啶衍生物21；然而，在不同条件下实现该构件环三聚的尝试并未成功。21 与氯化铜的反应允许分离出乙炔铜 22，其聚集成包含四个铜 (I) 离子如 [23·Cu]+ 的三角形三聚复合物，如通过 ESI 质谱监测。