Triaryl Oxonium Ions: A mild strategy to functionalised arynes.

洋葱离子是合成化学中普遍存在的试剂。碘盐和硫离子和磷离子的叶立德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更有限。三烷基氧离子最早发现于1937年，是由环氧化物与乙醚在Lewis酸存在下反应而发现的，此后它们一直被用作强烷化剂。三芳基氧离子最早出现于1957年，与烷基离子相比表现出更高的稳定性，并经历了亲电的芳香取代反应。尽管如此，它们在很大程度上已经被遗忘了--事实证明，三芳氧离子在化学文献中极其罕见，不到10个不同的支架。此外，还没有关于它们被用作芳烃前体的报道，尽管在碱性条件下芳烃的形成是一种被提出的分解途径，而其他洋离子，如碘盐，被用于生成芳烃。碘离子在强碱性条件下或与相邻的三甲基硅基形成芳烃，可被氟化物激活。氟化物活化三甲基硅芳基三氟酸酯是最常见的生成邻芳烃的方法，但敏感官能团通常安装在末端，因为它们不符合安装反应部分所需的条件。这种不相容、合成挑战以及氟化物或强碱的使用导致芳炔很少用于复杂分子和后期官能化，尽管它们具有产生复杂性和不同反应的合成潜力。我们的目标是开发一种温和且可扩展的合成路线来获得所需的氧离子。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体系，以扩大芳烃化学的研究范围。此外，氧离子的高离开基团能力应该允许我们从传统方法失败的底物中生成芳烃。提高芳烃化学的效率和范围的追求与EPSRC在化学科学中100%高效合成的重大挑战密切相关。人们还希望，正在开发的方法将被用于帮助合成化学家构建复杂的分子，从多环芳烃到药物发现等等。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.