Oxonium ions for the synthesis of strained alkynes and allenes

该项目的目标是开发用于功能化应变炔烃和联烯的氧离子前体，这两种化合物是快速合成复杂有机分子的有用合成子。氧离子是很好的离开基团，这在Hellwinkel和Tolstaya使用三芳基氧离子作为芳烃前体的简要调查中得到了利用。最近，Smith和Burton报告了使用二苯并呋喃氧离子作为工作台稳定盐，在非常温和的条件下生成芳烃。Fujita和Okuyama证明了相应的烯基碘盐与各种温和的碱可以生成环己炔，这种生成环己炔的方法已经被Carreira推广用于天然产物的合成。环己烯、1，2-环己二烯和环戊炔的另一种流行的方法以及最近的1，2，3-环己三烯的生成方法是由Garg小组报告的小林三硅基三氟酸盐方法。这是目前合成应变炔烃和累积烯的最新技术。鉴于从氧离子生成芳烃的研究最近才被深入研究，而且是在非常温和的条件下发生的，因此研究用于合成其他应变炔烃和烯的氧离子前体是合适的。该项目首先合成了二苯并呋喃氧离子前驱体，即无官能化的环己炔、环戊炔、1，2-环己二烯、1，2-环戊二烯和1，2，3-环己三烯。然后，将调查这些应变的炔烃和烯的生成和捕获。接下来，我们将研究应变烯/烯形成时官能团的耐受性。评估官能团耐受性的最直接方法将是评估一系列取代基在四酮起始材料上的相容性，包括硝基、醛、酮、酯、腈、醇、胺等官能团。随着对未官能化的应变炔烃和烯的形成和捕获的深入研究，该策略将扩展到官能化变体。也许最有趣的和潜在的最有可能合成有用的官能化的应变炔/烯是环己酮/环戊酮和相应的α，β，β，伽马不饱和环己酮/环戊酮。对这些化合物的合成方法应该是直截了当的，并允许对这些不寻常的应变炔进行研究，但有关这些方面的报道很少。

This project’s aim is the development of oxonium ion precursors for functionalised strained alkynes and allenes, which are useful synthons for the rapid synthesis of complex organic molecules. Oxonium ions are excellent leaving groups and this has been leveraged in a brief investigation of the use of triaryl oxonium ions as aryne precursors by Hellwinkel and Tolstaya. More recently, Smith and Burton have reported the use of dibenzofuranyl oxonium ions as bench-stable salts that generate arynes under very mild conditions. Fujita and Okuyama demonstrated that cyclohexyne could be generated from the corresponding alkenyl iodonium salts with a variety of mild bases, and this method of cyclohexyne generation has been popularised by Carreira for use in natural product synthesis. The other popular method for cyclohexyne, 1,2-cyclohexadiene and cyclopentyne, and most recently, 1,2,3-cyclohexatriene generation has been the Kobayashi silyl triflate method reported by the Garg group. This is the current state-of-the-art in the synthesis of strained alkynes and cumulenes. Given that aryne generation from oxonium ions has only recently been explored in depth and occurs under very mild conditions, it is fitting to investigate oxonium ion precursors for the synthesis of other strained alkynes and allenes. This project starts with the synthesis of the dibenzofuranyl oxonium ion precursors of unfunctionalised cyclohexynes, cyclopentynes, 1,2-cyclohexadienes, 1,2-cyclopentadienes, and 1,2,3-cyclohexatrienes. Afterwards, the generation and trapping of these strained alkynes and allenes will be investigated. Next, the functional group tolerance of the formation of strained alkynes/allenes will be investigated. The most straightforward method for assessing the functional group tolerance will be to evaluate the compatibility of a range of substituents on the tetralone starting materials, including functional groups such as nitro, aldehyde, ketone, ester, nitrile, alcohol, amine etc. With the formation and trapping of unfunctionalized strained alkynes and allenes thoroughly explored, the strategy will be expanded to the functionalized variants. Perhaps the most interesting and potentially the most synthetically useful functionalized strained alkynes/allenes are the cyclohexynones/cyclopentynones and corresponding alpha,beta,beta,gamma-unsaturated cyclohexanones/cyclopentanones. The synthetic approach to these should be straightforward and allow the study of these unusual strained alkynes, of which little has been reported.