Triaryl Oxonium Ions: A mild strategy to functionalised arynes.

铵离子是合成化学中普遍存在的试剂。碘盐和硫磷离子的酰化物是非常宝贵的合成工具。然而，氧离子的形成及其在合成中的应用明显受到限制。三烷基氧鎓离子是1937年在路易斯酸的存在下由环氧化物与醚反应发现的，从那时起它们就被用作强烷基化剂。三芳基氧鎓离子于1957年首次出现，与烷基离子相比，它表现出更高的稳定性，并能进行亲电芳香取代反应。尽管如此，它们在很大程度上被遗忘了——事实证明，三芳基氧鎓离子在化学文献中非常罕见，只有不到10种不同的支架。此外，尽管在基本条件下形成任何炔是一种被提出的分解途径，并且其他的离子，如碘盐，被用于生成任何炔，但没有报道将它们用作任何炔前体。碘离子在强碱性条件下或与相邻的可被氟活化的三甲基硅基形成芳炔。三甲基硅芳基三氟化酯的氟化活化是生成邻芳炔最常用的方法，然而，敏感官能团通常安装在末端，因为它们与安装反应性部分所需的条件不相容。这种不相容性、合成挑战以及氟化物或强碱的使用导致芳烃很少用于复杂分子和后期功能化，尽管它们具有合成复杂性和多种反应性的潜力。我们的目标是开发一种温和和可扩展的合成途径，以获得所需的氧鎓离子。我们随后将测试它们在基本条件下生成芳烃的能力，优化它们的反应性，然后将其应用于具有敏感官能团的复杂系统，以扩大芳烃化学的范围。此外，氧离子的高离去基能力应该允许我们从传统方法失败的底物中生成芳炔。追求提高任何化学的效率和范围与EPSRC在化学科学中100%高效合成的重大挑战密切相关。还希望正在开发的方法将用于帮助合成化学家构建从多芳烃到药物发现等复杂分子。该项目属于EPSRC物理化学（合成有机化学）研究领域。

Onium ions are ubiquitous reagents in synthetic chemistry. Iodonium salts and ylides of sulfonium and phosphonium ions are invaluable synthetic tools. However, the formation of oxonium ions and their use in synthesis is significantly more limited. Trialkyl oxonium ions were first discovered in 1937 by the reaction of an epoxide with an ether in the presence of a Lewis acid and they have been used as strong alkylating agents ever since. Triaryl oxonium ions first emerged in 1957 and exhibit enhanced stability compared with their alkyl counterparts and undergo electrophilic aromatic substitution reactions. Despite this, they have largely been forgotten - demonstrated by the fact that triaryl oxonium ions are incredibly rare in the chemical literature with fewer than 10 distinct scaffolds. Furthermore, there are no reports of them being used as aryne precursors despite aryne formation being a proposed decomposition pathway under basic conditions and other onium ions, such as iodonium salts, being used for aryne generation. Iodonium ions form arynes under strongly basic conditions or with adjacent trimethylsilyl groups that can be activated by fluoride. Fluoride activation of trimethylsilylaryltriflates is the most common method to generate o-arynes, however, sensitive functional groups are generally installed at the end as they are not compatible with the conditions require to install the reactive moieties. This incompatibility, synthetic challenges and the use of fluoride or strong bases results in arynes being rarely used in complex molecules and late stage functionalisation despite their synthetic potential for complexity generation and diverse reactivity.We aim to develop a mild and scalable synthetic route to the desired oxonium ions. We would subsequently test their ability to generate arynes under basic conditions, optimise their reactivity and then apply it to complex systems with sensitive functional groups to expand the reach of aryne chemistry. Furthermore, the high leaving group ability of oxonium ions should allow us to generate arynes from substrates where the traditional methodology fails. Pursuit of increasing the efficiency and scope of the aryne chemistry closely aligns with the EPSRC grand challenge of 100% efficient synthesis in the chemical sciences. It is also hoped that the methodology being developed will be utilised to aid synthetic chemists constructing complex molecules from polyaromatic hydrocarbons to drug discovery and beyond. This project falls within the EPSRC Physical Chemistry (Synthetic Organic Chemistry) research area.