A Case ofanti Carbolithiation of Alkynes Resulting from Intramolecular Lithium Coordination
作者:Catherine Fressigné、Anne-Lise Girard、Muriel Durandetti、Jacques Maddaluno
DOI:10.1002/chem.200701834
日期:2008.6.9
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
已通过实验和理论研究了锂化炔丙基醚2分子内碳锂化的机理。结果表明,当量正丁基锂对1的作用足以触发卤素-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基锂。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:O-Li相互作用在整个闭环过程中一直存在,驱动阳离子到最终烯烃的E位。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。用烯丙基1d重复该实验。在这种情况下,一当量的正丁基锂就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