NEW HALOGENATION REAGENT SYSTEMS USEFUL FOR THE MILD ONE-STEP CONVERSION OF ALCOHOLS INTO IODIDES OR BROMIDES
NEW HALOGENATION REAGENT SYSTEMS USEFUL FOR THE MILD ONE-STEP CONVERSION OF ALCOHOLS INTO IODIDES OR BROMIDES
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DOI：
10.1021/jo00261a032
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发表时间：
1988-12-23
影响因子：
3.6
通讯作者：
SAMUELSSON, B
中科院分区：
文献类型：
--
作者：
CLASSON, B;LIU, ZC;SAMUELSSON, B
烷基卤化物，特别是碘化物和溴化物，用于离子或自由基碳-碳偶联反应。它们通常是取代反应、消除和重排反应中的中间体。醇也很容易通过卤化物转化为脱氧衍生物。烷基卤化物可以通过不同的程序从相应的醇中很容易地获得。对于醇直接转化为烷基溴化物或碘化物，磷基试剂是最常用的。Rydon等人在20世纪50年代引入了以三苯基亚磷酸盐为基础的试剂，如甲基三苯氧基碘化膦和碘代三苯氧基碘化膦，用于醇的碘化。1这些试剂现在一般已被三苯基膦与卤素源结合使用，如四溴碳、2-溴代丁二酰亚胺或4-碘代丁二酰亚胺。最近，三苯基膦与三碘-咪唑，或碘和咪唑，或三溴咪唑一起使用，提供了多羟基化合物的高产率和选择性。4所有这些系统都需要较高的温度和较长的反应时间。这些试剂体系遇到的一个主要困难是，三苯基膦及其氧化物很难通过沉淀和/或层析以外的方法从反应混合物中去除，这除了繁琐外，还会导致产率降低。这在大规模合成中尤其不方便。这项工作的目的是寻找新的碘化和溴化试剂体系，在该体系中，磷基试剂和产品可以通过萃取从有机相中去除。根据这一要求，设计了两套卤化试剂系统。它们由碘(或溴)、咪唑和下列试剂之一组成：A，氯二苯基膦(CDP)(1)；或B，[p-(二甲氨基)苯基]二苯基膦5[(p-Me2NC6H4)P(Ph)2](DAPDP)(2)。用这些体系对醇进行卤化反应，可以在温和的条件下得到高产率的产品，在工作过程中，含磷的产品会从有机相中提取成碱性(A)或酸性(B)水相。卤代试剂体系A：Cl-P(Ph)2+I2(Br2)+咪唑
Alkyl halides, especially iodides and bromides, are used for ionic or radical carbon-carbon coupling reactions. They are often the intermediates of choice in substitution re-actions, eliminations, and rearrangements. Alcohols are also easily transformed into the deoxy derivatives via the halides. Alkyl halides are readily available from the cor-responding alcohols by different procedures. For the direct conversion of alcohols into alkyl bromides or iodides, phosphorus-based reagents are the most commonly used. Rydon et al., in the 1950s, introduced triphenyl phos-phite based reagents such as methyltriphenoxy-phosphonium iodide and iodotriphenoxyphosphonium iodide for the iodinationof alcohols. 1 These reagents have now generally been replaced by triphenylphosphine in combination with a halogen source such as carbon tetrabromide, 2 IV-bromosuccinimide or iV-iodosuccinimide. 3 Recently triphenylphosphine together with triiodo-imidazole, or iodine and imidazole, or tribromoimidazole, have been used, giving high yields coupled with selectivity for polyhydroxy compounds. 4 All of these systems gen-erally require elevated temperatures and long reaction times. A major difficulty experienced with these reagent systems is due tothe fact that triphenylphosphine and its oxide are difficult to remove from the reaction mixture by means other than precipitation and/or chromatography, which besides being cumbersome results in reduced yield. This is especially inconvenient in large-scale synthesis. The aim of this work was to find new iodination and bromination reagent systems in which the phosphorus-based reagents and products could be removed from the organic phase by extraction. Two halogenation reagent systems were designed with this requirement. They consist of iodine (or bromine), imidazole and one of the following reagents: A, chlorodiphenylphosphine (CDP)(1); or B,[p-(dimethylamino) phenyl] diphenylphosphine5 [(p-Me2NC6H4) P (Ph) 2](DAPDP)(2). Halogenation of alco-hols with these systems gives products in high yields under mild conditions, and the phosphorus-containing products are extracted from the organic phase into a basic (for A) or acidic (for B) aqueousphase during workup. halogenation reagent systems A: Cl-P (Ph) 2+ I2 (Br2)+ imidazole