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首页> 外文期刊>Chemistry: A European journal >A case of anti carbolithiation or Alkynes resulting from intramolecular lithium coordination
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A case of anti carbolithiation or Alkynes resulting from intramolecular lithium coordination

机译：一例因分子内锂配位引起的抗碳石化或炔烃

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The mechanism of the intramolecular carbolithiation of lithiated propargylic ether 2 has been investigated both experimentally and theoretically. The results show that the action of one equivalent of n-butyllithium on 1 is sufficient to trigger halogen-lithium exchange and the subsequent heterocyclization step. Interestingly, the reaction stops at the stage of dihydrobenzofuran 6; no spontaneous elimination of lithium ethylate was observed. The fact that the E configuration of this adduct was exclusively produced suggests that the reaction proceeds by following an unprecedented anti addition on the alkyne. According to DFT calculations, this unexpected outcome is related to the intramolecular coordination of the lithium by one oxygen atom of the terminal acetal appendage: the O-Li interaction, which persists all along the ring-closure process, drives the cation to the E site of the final olefin. The calculations also show that in the absence of this coordination (as in conformers B and C of acetal 2), the Z olefin that results from a classical syn addition of the aryllithium should be obtained. The experiments were repeated with allene Id. In this case, one equivalent of n-butyllithium suffices to trigger not only the exchange and the cyclization, but also the final elimination of lithium ethoxide. The DFT results indicate that the intramolecular addition of the original aryllithium on the central carbon atom of the allene 2b yields the expected benzofuran skeleton 3b, which bears a lithiated lateral chain at the 3-position. Both cyclizations go through low-lying transition states, as is expected for rapid reactions at low temperature.
机译：已通过实验和理论研究了锂化的炔丙基醚2分子内碳锂化的机理。结果表明，一当量正丁基锂对1的作用足以引发卤素-锂交换和随后的杂环化步骤。有趣的是，该反应在二氢苯并呋喃6的阶段停止。没有观察到自发消除乙酸乙酯。仅生成该加合物的E构型的事实表明，通过在炔烃上进行空前的抗加成反应来进行反应。根据DFT计算，这种意外的结果与末端缩醛附件的一个氧原子对锂的分子内配位有关：在闭环过程中一直存在的O-Li相互作用将阳离子驱至E位最终烯烃的含量。计算还表明，在没有这种配位的情况下（如乙缩醛2的构象异构体B和C），应获得由芳基锂的经典同加成产生的Z烯烃。使用Allene Id重复实验。在这种情况下，一当量的正丁基锂不仅足以引发交换和环化，而且最终消除了乙醇锂。 DFT结果表明，在芳基2b的中心碳原子上分子内加成原始的芳基锂产生了预期的苯并呋喃骨架3b，其在3-位带有锂化的侧链。如在低温下快速反应所预期的，两个环化都经历低位的过渡态。

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