Hydride shift generated oxonium ions:: Evidence for mechanism and intramolecular trapping experiments to form trans THF derivatives
Hydride shift generated oxonium ions:: Evidence for mechanism and intramolecular trapping experiments to form trans THF derivatives
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DOI：
10.1002/anie.200705340
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Churchill, Gwydion H.
中科院分区：
文献类型：
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作者：
Donohoe, Timothy J.;Williams, Oliver;Churchill, Gwydion H.
鉴于天然产物中四氢呋喃（THF）环的数量和种类繁多（许多具有有趣和有用的生物活性），我们致力于开发新方法来制备这些杂环，并控制立体和区域化学的各个方面。[1]在这方面，我们最近报道了将邻位醇及其衍生物催化氧化环化到邻近烯烃上，从而形成顺式-2，5-二取代的THF环的一般方法（方案1）。[2]该反应涉及两个杂原子在双键上的立体定向合成加成，这意味着环化的立体化学结果是可控的。使用这种过渡金属催化的氧化环化反应形成THF衍生物的限制之一是强烈的和固有的偏好形成顺式THF杂环。[3]这种偏好的起源在于环化前体和锇之间的配位的二齿性质，其对过渡结构的几何形状施加限制并强制实施顺式-2，5-立体选择性。最近，我们的注意力转向了制备反式-2，5-二取代THF衍生物的方法，因为这些基序通常存在于天然产物靶标中。改进催化氧化环化反应以直接形成反式THF环的尝试尚未被实施。
Given the large number and variety of tetrahydrofuran (THF) rings in natural products (many with interesting and useful biological activity), we are engaged in the development of new methods to prepare these heterocycles with control of all aspects of stereo-and regiochemistry.[1] In this regard, we have recently reported a general method for the catalytic oxidative cyclization of vicinal alcohols, and derivatives thereof, onto proximal alkenes, thus forming cis-2, 5-disubstituted THF rings (Scheme 1).[2] The reaction involves stereospecific syn addition of two heteroatoms across the double bond, meaning that the stereochemical outcome of the cyclization is controllable.One of the restrictions of using such transition-metalcatalyzed oxidative cyclizations to form THF derivatives is the strong and inherent preference to form cis THF heterocycles.[3] The origins for this preference lie in the bidentate nature of coordination between the cyclization precursor and osmium, which places constraints upon the geometry of the transition structure and enforces cis-2, 5-stereoselectivity. Recently, our attention turned to methods for preparing trans-2, 5-disubstituted THF derivatives, because these motifs are commonly found in natural-product targets. Attempts to modify the catalytic oxidative cyclization reaction to form trans THF rings directly have not been