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首页> 外文期刊>Current Organic Synthesis >A Simplified Protocol for Routine Chemoselective Syntheses of Piperazines Substituted in the 1-Position by an Electron Withdrawing Group
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A Simplified Protocol for Routine Chemoselective Syntheses of Piperazines Substituted in the 1-Position by an Electron Withdrawing Group

机译：常规电子选择性合成哌嗪在1位上被电子吸收基团取代的简化协议

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摘要

We report a simplified protocol for the routine direct chemoselective preparation of various piperazines substituted in the 1-position by an electron withdrawing group. These syntheses are based on the reaction of piperazine-1-ium cation with different electrophilic reagents such as acyl chlorides, anhydrides, sulfonyl chlorides, carbamoyl chlorides, and nitrourea as well. Piperazine-1-ium cation was chosen because the reactions of piperazine with electrophilic reagents in different solvents at usual temperatures are not chemoselective and provide mixtures comprising 1-substituted, 1,4-disubstituted and unsubstituted piperazine as well. Simultaneously, the mono-protonation of piperazine is the simplest synthetic method for its protection/deprotection in comparison with the currently used mono-benzylation, mono-Boc-protection, etc. Computer modeling of acid-base equilibria for piperazine and model 1-acetylpiperazine was used as the basis for the prediction of reaction conditions suitable for the synthesis. It was found that for in situ generating of starting piperazine-1-ium cation from piperazine the application of acetic acid as reaction medium or the chemisorption of piperazine on weakly acidic cation-exchanger resin were highly acceptable in terms of both reaction times and yields. The using of resin supported piperazine-1-ium cation in reaction with carboxylic anhydrides or nitrourea is an example of the solid phase synthesis with ionically bonded substrate. Furthermore, syntheses in acetic acid medium were effectively catalyzed by Cu+, Cu2+ or Al3+ ions supported on weakly acidic cation-exchanger resin as well. Finally, it was observed that application of the solid support metal catalysis afforded target products in shortened reaction times and in 82-95% yields.
机译：我们报告了一种简化的协议，用于常规直接化学选择性制备各种在1位被吸电子基团取代的哌嗪。这些合成是基于哌嗪-1-鎓阳离子与不同的亲电试剂如酰氯，酸酐，磺酰氯，氨基甲酰氯和硝基脲的反应。选择哌嗪-1-鎓阳离子是因为哌嗪与亲电试剂在常温下在不同溶剂中的反应不是化学选择性的，并且提供了包括1-取代的，1,4-二取代和未取代的哌嗪的混合物。同时，与目前使用的单苄基化，mono-Boc保护等相比，哌嗪的单质子化是对其保护/脱保护的最简单的合成方法。哌嗪和1-乙酰基哌嗪模型的酸碱平衡的计算机模型作为预测适合合成的反应条件的基础。已经发现，对于从哌嗪原位生成起始哌嗪-1-鎓阳离子而言，就反应时间和产率而言，乙酸作为反应介质的应用或哌嗪在弱酸性阳离子交换树脂上的化学吸附是高度可接受的。与羧酸酐或硝基脲反应中使用树脂负载的哌嗪-1-鎓阳离子是具有离子键合底物的固相合成的一个实例。此外，乙酸介质中的合成也可以通过弱酸性阳离子交换树脂上负载的Cu +，Cu2 +或Al3 +离子有效催化。最后，观察到固体载体金属催化的应用以缩短的反应时间和82-95％的产率提供了目标产物。

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