FORMATION OF FUNCTIONALIZED DIHYDROBENZOFURANS BY RADICAL CYCLIZATION
FORMATION OF FUNCTIONALIZED DIHYDROBENZOFURANS BY RADICAL CYCLIZATION
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DOI：
10.1021/ja00279a038
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发表时间：
1986-09-17
影响因子：
15
通讯作者：
BECKWITH, ALJ
中科院分区：
文献类型：
--
作者：
MEIJS, GF;BECKWITH, ALJ
在Me2SO溶液中，用（II）溴化铜或氯化物处理arenediazonium四氟硼酸盐4a和4b，可以得到环化的光环化合物5a、5b和5c，收率很高。铜(I)氰化/吡啶对4b的环闭合产生腈5d。用苯硫代酸或丁硫代酸离子在Me2SO中处理4a或4b也可生成二氢苯并呋喃衍生物。提出了涉及中间芳基自由基环化的链机制。邻位取代基在相对于自由基中心的5,6或6,7位置上含有双键的芳基自由基在外显模式下进行快速的区域选择性环化（1 - * 2）。以前，这种自由基是通过用三丁基氢化锡处理适当的碘化芳基而产生的，用于动力学研究。3然而，这种方法对制备工作没有吸引力，因为反应混合物需要稀释以确保环化产物的优势，锡化合物的完全去除是困难的，5* 7引发是不可靠的，所需的大量三丁基氢化锡是昂贵的。因此，我们寻求替代方法来影响合适的芳基自由基的环闭合。特别令人感兴趣的是那些既可能产生治疗作用又可能在环化自由基中心引入新的官能团(X)的方法（方案一）。这种反应将产生适于进一步细化的功能化产物（例如，3）。所选择的自由基前体是四氟硼酸重氮。重氮盐的大量反应被认为涉及自由基中间体，8* 10和四氟硼酸盐容易制备，相对稳定，易于处理和纯化。本文研究了硫代脱氮剂和铜基“Sandmeyer”脱氮剂诱导的o-（2-丙烯氧基）-苯二氮四氟硼酸铵（4a）和o-（2-甲基-2-丙烯基）氧-苯二氮四氟硼酸铵（4b）的闭环反应。
Treatment of the arenediazoniumtetrafluoroborates 4a and 4b in Me2SO solution with copper (II) bromide or chloride gave thecyclized halo compounds 5a, 5b, and 5c in good yield. Copper (I) cyanide/pyridine effected ring closure of 4b to afford the nitrile 5d. Dihydrobenzofuran derivatives were also formed on treatment of 4a or 4b with benzenethiolate or butanethiolate ionin Me2SO. Chain mechanisms involving cyclization of an intermediate aryl radical are suggested.Aryl radicals with ortho substituents containing double bonds in the 5, 6 or 6, 7 positionsrelative to the radical center undergo rapid, regioselective cyclization (1—* 2) in the exo mode. 2* 4 Previously, such radicals had been generated for kinetic studies by treating the appropriate aryl iodidewith tri-n-butyltin hydride. 3 This procedure, however, was unattractive for preparative work since reactionmixtures needed to be dilute to ensure the predominance of the cyclized product, complete removal of the tin compounds was difficult, 5* 7 initiation was unreliable, and the considerable quantity of tributyltin hydride required was expensive. We sought, therefore, alternative methods for effecting the ring closure of suitable aryl radicals. Procedures which were likely both to generate theradical and to introduce a new functional group (X) at thecyclized radical center (Scheme I) were of especial interest. Such reactions would afford functionalized products (eg, 3) suitable for further elaboration. The radical precursors chosen for study were diazonium tet-rafluoroborates. A large number of reactions involving diazonium salts are thought to involve free-radical intermediates, 8* 10 and the tetrafluoroborate salts are easily prepared, are relatively stable, and are convenient to handle and purify. This paper describes ring closures of o-(2-propenyloxy)-benzenediazonium tetrafluoroborate (4a) and o-((2-methyl-2-propenyl) oxy) benzenediazonium tetrafluoroborate (4b) induced by thiodediazoniation agents and copper-based “Sandmeyer” dediazoniation reagents.