Department of Chemistry and Chemical Biology, Baker Laboratory , Cornell University , Ithaca , New York 14853-1301 , United States.
J Org Chem. 2019 Sep 6;84(17):10860-10869. doi: 10.1021/acs.joc.9b01428. Epub 2019 Aug 22.
Eliminations of alkyl halides by sodium diisopropylamide (NaDA) in tetrahydrofuran (THF)/hexane or THF/-dimethylethylamine (DMEA) solutions are facile and complementary to analogous reactions of lithium diisopropylamide in THF. Rate studies show a dominance of monomer-based metalations and prevalent secondary-shell solvation effects overlaid on primary-shell effects. 1-Halooctanes exclusively undergo elimination rather than substitution. Rate and isotopic labeling studies on 1-bromooctane reveal an E2-like elimination pathway via trisolvated NaDA monomer. By contrast, 1-chlorooctane is eliminated via disolvated monomer through a carbenoid mechanism. -2-Norbornyl chloride and bromide are also eliminated via disolvated monomer; a syn E2 mechanism is inferred for these substrates. The and -4--butylcyclohexyl bromides show a preference for the elimination of the cis isomer (/ = 10). Rate and isotopic labeling studies are consistent with a trans-diaxial E2 elimination via trisolvated monomer for the cis isomer and a carbenoid mechanism via disolvated monomer for the trans isomer. Vicinal haloethers show substrate-dependent reactivities, affording alkynes and enol ethers. -1-Bromo-2-methoxycyclohexane provides enol ether 1-methoxycyclohexene, while -1-bromo-2-methoxycyclooctane provides dimeric products consistent with fleeting cycloocta-1,2-diene (cyclic allene), which was fully characterized as two conformers.
在四氢呋喃（THF）/己烷或 THF/-二甲基乙胺（DMEA）溶液中，通过双异丙基胺钠（NaDA）消除卤代烷是容易的，并且与锂双异丙基胺在 THF 中的类似反应互补。速率研究表明，单体基金属化作用和普遍的次级壳溶剂化效应占据主导地位，叠加在初级壳效应之上。1-卤代辛烷仅经历消除而不是取代。1-溴代辛烷的速率和同位素标记研究表明，通过三溶剂化的 NaDA 单体，存在类似于 E2 的消除途径。相比之下，1-氯代辛烷通过溶剂化单体通过卡宾机理消除。-2-降冰片基氯化物和溴化物也通过溶剂化单体消除；推断这些底物通过顺式 E2 机制消除。顺式异构体（/ = 10）优先消除 4--正丁基环己基溴化物。速率和同位素标记研究与顺式异构体通过三溶剂化单体的反式双轴向 E2 消除以及反式异构体通过溶剂化单体的卡宾机理一致。偕二卤代醚表现出与底物相关的反应性，提供炔烃和烯醇醚。-1-溴-2-甲氧基环己烷提供烯醇醚 1-甲氧基环己烯，而-1-溴-2-甲氧基环辛烷提供二聚产物，与短暂的环辛-1,2-二烯（环状丙烯）一致，该物质完全被描述为两种构象。
