《自然》:化学家合成并表征了具有立体氧原子中心的新型螺旋手性氧鎓离子 精选
2023-3-25 09:25




Mechanistic overview of enantiomerization of oxepin-containing oxonium ion. a, B3LYP-D3(BJ)/6-31+G(d,p) computed Gibbs energy profile for enantiomerization demonstrates that the process consists of a high barrier oxygen inversion and a low barrier conformational relaxation of the seven-membered ring. b, Geometrical measurements of TS B. ϕ=(C6–C7–C8–C9) dihedral angle. c, Computed change in ring strain (ΔEdist) in highlighted rings in xanthene and dihydrodibenzooxepine oxonium ions on going from GS to TS. The relative energies of truncated xanthene and dihydrodibenzooxepine substructures are computed at geometries taken from the parent oxonium ion. d, Comparison of computed barriers to inversion show that triaryloxonium ions have higher barriers to inversion than corresponding triaryl amines (B3LYP-D3(BJ)/6-31+G(d,p)). Grel =relative Gibbs free energy. ‡=transition state. Credit: Nature (2023). DOI: 10.1038/s41586-023-05719-z

尽管“科学网”对于“螺旋手性氧离子中立体氧的控制”已经有所介绍,但是过于简要,为了便于读者能够较为全面了解情况,本文根据物理学家组织网(Phys.org2023322日报道,对于英国牛津大学(University of Oxford, UK)的一组化学家与美国科罗拉多州立大学(Colorado State University, Ft. Collins, CO, USA)的研究人员合作,首次合成并表征了一种具有立体氧原子中心的新型螺旋手性氧鎓离子(Chemists synthesize and characterize novel helically chiral oxonium ion with a stereogenic oxygen atom center)的报道编译如下,仅供参考。相关研究结果于2023315日已经在《自然》(Nature)杂志网站发表——Owen SmithMihai V PopescuMadeleine J HindsonRobert S PatonJonathan W BurtonMartin D Smith. Control of stereogenic oxygen in a helically chiral oxonium ion. Nature, 2023. 615 (7952): 430-435. DOI: 10.1038/s41586-023-05719-z.  Epub 2023 Mar 15. https://www.nature.com/articles/s41586-023-05719-z

在他们发表在《自然》(Nature)杂志上的研究论文中,该小组研究了氧鎓离子(oxonium ion),提出了一种制造具有手性中心的五环氧鎓盐(pentacyclic oxonium salt)的方法。

手性有机分子一般都有一个基于碳原子的光学中心,尽管已经使用三价氮做了一些工作。以前的研究人员已经研究过使用氧原子(oxygen atom)的可能性,但这样做的方法被认为是特别困难的,因此尚未进行研究。在这项新的努力中,研究小组在研究了氧鎓离子后发现,三芳基氧鎓离子可能被用来制造一种稳定的手性化合物,其中心是氧原子,因为它们往往是稳定的、可隔离的和结晶的。

研究小组一开始就指出,如果将这种化合物嵌入一个合适的、灵活的环系统中,就可以产生一种化合物,因为它可以减缓反转。然后他们开始利用量子力学理论研究合适的候选对象。所以他们用一个带正电的氧原子作为中心原子。氧鎓离子是由吡啶-2-基取代的1,4-苯并二噁烷衍生物(pyridine-2-yl-substituted 1,4-benzodioxane derivative)用三氟甲磺酸(triflic acid)质子化得到的。然后,研究小组添加了三个芳香取代基,使用七原子和五原子环连接在一起。结果是一种三维化合物,具有缓慢的外消旋作用。


本研究得到了英国工程与物理科学研究委员会(EPSRC)提供生物学和医学合成博士训练中心提供的奖学金{ Centre for Doctoral Training in Synthesis for Biology and Medicine (EP/ L015838/1)}DTP奖学金{ DTP studentship (EP/T517811/1; project no. 2446204)}、美国国家科学基金会(NSF CHE-1955876, ACI-1532235 and ACI-1532236)、美国科罗拉多大学博尔德分校(University of Colorado Boulder)和科罗拉多州立大学(Colorado State University)的极端科学与工程探索环境(Extreme Science and Engineering Discovery Environment简称XSEDE)配套经费(TG-CHE180056)的资助。



The control of tetrahedral carbon stereocentres remains a focus of modern synthetic chemistry and is enabled by their configurational stability. By contrast, trisubstituted nitrogen1, phosphorus2 and sulfur compounds3 undergo pyramidal inversion, a fundamental and well-recognized stereochemical phenomenon that is widely exploited4. However, the stereochemistry of oxonium ions—compounds bearing three substituents on a positively charged oxygen atom—is poorly developed and there are few applications of oxonium ions in synthesis beyond their existence as reactive intermediates5,6. There are no examples of configurationally stable oxonium ions in which the oxygen atom is the sole stereogenic centre, probably owing to the low barrier to oxygen pyramidal inversion7 and the perception that all oxonium ions are highly reactive. Here we describe the design, synthesis and characterization of a helically chiral triaryloxonium ion in which inversion of the oxygen lone pair is prevented through geometric restriction to enable it to function as a determinant of configuration. A combined synthesis and quantum calculation approach delineates design principles that enable configurationally stable and room-temperature isolable salts to be generated. We show that the barrier to inversion is greater than 110 kJ mol−1 and outline processes for resolution. This constitutes, to our knowledge, the only example of a chiral non-racemic and configurationally stable molecule in which the oxygen atom is the sole stereogenic centre.





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