Migrating alkynes in vinylidene carbenoids: An unprecedented route to polyynes
Migrating alkynes in vinylidene carbenoids: An unprecedented route to polyynes
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DOI：
10.1021/ja005557t
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发表时间：
2000-11-01
影响因子：
15
通讯作者：
Tykwinski, RR
中科院分区：
文献类型：
--
作者：
Eisler, S;Tykwinski, RR
亚烷基卡宾（1，M）或卡宾（2）的Fritsch-Buttenberg-Wiechell（FBW）重排1是合成乙炔的成熟方法。[2]这种转换已经应用于许多体系，其中1或2中的迁移基团R1或R2是芳基或杂芳基部分、氢原子或烷基（对于这些基团，1，5-CH插入是不可能的）。[3]在许多情况下，这种重排在形成环状炔属体系方面特别有效，否则很难合成。[4]然而，据我们所知，在FBW重排反应中，还没有发现炔发生迁移的现象，我们的研究表明，炔部分很容易通过一个中间的亚烷基卡宾/类卡宾物种发生1，2-迁移。在这些反应中，n-BuLi和1，1-二溴-2，2-二乙炔基乙烯之间的锂-卤素交换引发炔迁移，并提供合成有用的产率的宽范围的多炔。二溴烯烃前体是容易获得的，并且可以策略性地官能化，以提供通过其他方法难以或不可能获得的多炔体系。5我们预期n-BuLi和适当的1，1-二溴烯烃之间的锂-卤素交换可以有效地产生必需的类卡宾中间体3。6事实上，中间体3（M）Li）先前已在低温下由4a、B（表1）中的其它化合物生成。7、8然而，在这些情况下没有报告卡宾形成的证据。我们对3的初始实验利用了更稳定的三异丙基甲硅烷基（TIPS）保护的4a。在-78 ℃下，向4a的THF溶液中加入少量的
The Fritsch-Buttenberg-Wiechell (FBW) Rearrangement1 of alkylidene carbenoids (1, M) metal) or carbenes (2) is a wellestablished method for the synthesis of acetylenes. 2 This transformation has been applied to numerous systems in which the migrating group in 1 or 2, R1 or R2, is an aryl or heteroaryl moiety, a hydrogen atom, or an alkyl group (for which 1, 5-CH insertion is impossible). 3 In many cases, this rearrangement has been particularly effective in the formation of cyclic acetylenic systems that are otherwise difficult to synthesize. 4 To our knowledge, however, alkynes have never been made to migrate in a FBW rearrangement.With this report we show that alkyne moieties readily undergo 1, 2-shifts via an intermediate alkylidene carbene/carbenoid species. In these reactions, lithium-halogen exchange between n-BuLi and 1, 1-dibromo-2, 2-diethynylethenes initiates alkyne migration and affords synthetically useful yields of a wide range of polyynes. The dibromoolefinic precursors are readily available and can be strategically functionalized in order to afford polyyne systems that are difficult or impossible to attain by other methods. 5 We expected that lithium-halogen exchange between n-BuLi and the appropriate 1, 1-dibromoolefin could effectively generate the requisite carbenoid intermediate 3. 6 In fact, intermediate 3 (M) Li) has been previously generated at low temperature by others from 4a, b (Table 1). 7, 8 Evidence of carbene formation, however, was not reported in these cases. Our initial experiments toward 3 utilized the more stable triisopropylsilyl (TIPS) protected 4a. To a solution of 4a in THF at-78 C was added a slight