Hypervalent iodine chemistry: New oxidation reactions using the iodosylbenzene-trimethylsilyl azide reagent combination. Direct alpha- and beta-azido functionalization of triisopropylsilyl enol ethers
Hypervalent iodine chemistry: New oxidation reactions using the iodosylbenzene-trimethylsilyl azide reagent combination. Direct alpha- and beta-azido functionalization of triisopropylsilyl enol ethers
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DOI：
10.1021/ja953906r
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发表时间：
1996-04-10
影响因子：
15
通讯作者：
Hulme, C
中科院分区：
文献类型：
--
作者：
Magnus, P;Lacour, J;Hulme, C
用PhIO/TMSN（3）/在-18至-15 ℃下快速（5分钟）处理三异丙基甲硅烷基（TIPS）烯醇醚，以高产率得到β-叠氮基TIPS烯醇醚，仅具有痕量的α-叠氮基加合物。该反应对温度变化非常敏感，α-途径在-78 ° C下有利，β-途径在-15 ° C至-20 ° C下有利。添加催化量的稳定自由基克里思（2，2，6，6-四甲基哌啶-N-氧基）显著降低了β-叠氮酮化反应并增加了α-叠氮酮化反应。提出了一个机制假说，提供了一个明确的区别α-和β-功能化途径。这两种反应之间的关键区别在于α-途径是叠氮基加成过程，而β-途径涉及离子脱氢。将不寻常的β-官能化反应扩展到其他三甲基甲硅烷基衍生物（TMSX）的努力是不成功的。试剂组合PhIO/TMSN（3）是我们发现的唯一一种导致清洁、高产率β-官能化的系统。用S、Se、P、As或Te取代碘的尝试没有产生活性氧化剂，尽管在二苯基碲氧化物的情况下，我们能够分离出稳定的结晶加合物双[叠氮基二苯基碲（IV）]氧化物。
Treatment of triisopropylsilyl (TIPS) enol ethers with PhIO/TMSN(3)/at -18 to -15 degrees C rapidly (5 min) gave beta-azido TIPS enol ethers in high yields, with only traces of the alpha-azido adduct. The reaction is very sensitive to temperature changes, with the alpha-pathway being favored at -78 degrees C and the beta-pathway at -15 to -20 degrees C. Addition of catalytic amounts of the stable radical TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) significantly reduced the beta-azidonation and increased the alpha-azidonation reaction. A mechanistic hypothesis is presented that offers a clear distinction between the alpha- and beta-functionalization pathways. The key difference between the two reactions is that the alpha-pathway is an azide radical addition process and the beta-pathway involves ionic dehydrogenation. Efforts to extend the unusual beta-functionalization reaction to other trimethylsilyl derivatives (TMSX) were unsuccessful. The reagent combination PhIO/TMSN(3) is the only system we have found that results in clean, high-yield beta-functionalization. Attempts to substitute iodine with S, Se, P, As, or Te did not result in an active oxidant, although in the case of diphenyltelluroxide we were able to isolate the stable crystalline adduct bis[azidodiphenyltellurium(IV)] oxide.