Intramolecular Polar [4⊕+2] Cycloadditions of Aryl-1-aza-2-azoniaallene Salts: Unprecedented Reactivity Leading to Polycyclic Protonated Azomethine Imines
Intramolecular Polar [4⊕+2] Cycloadditions of Aryl-1-aza-2-azoniaallene Salts: Unprecedented Reactivity Leading to Polycyclic Protonated Azomethine Imines
复制标题
DOI：
10.1002/anie.201306553
复制
发表时间：
2013-12-09
影响因子：
16.6
通讯作者：
Brewer, Matthias
中科院分区：
文献类型：
--
作者：
Bercovici, Daniel A.;Ogilvie, Jodi M.;Brewer, Matthias
与涉及不带电荷或偶极组分的环加成反应相比，其中一个反应伙伴是离子的极环加成反应不太常见，但通常更容易发生。[1]例如，尽管涉及作为4π组分的苯乙烯亚单位的[4+2]环加成反应通常需要反应性的双烯烃或苛刻的反应条件才能进行，[2]波瓦罗夫反应是N-芳基锂离子与富含电子的烯烃的逐步[3][4+2]环加成反应，在室温或更低的温度下容易发生。5]在极性环加成反应的离子伙伴中存在的电荷通常是由于杂原子的存在，这些体系可以提供通向杂环产物的有用途径，[1a]这是生物活性分子中普遍存在的支架。[6]虽然未带电的杂烯已被广泛用于制备杂环化合物，但阳离子杂烯受到的关注较少。为此，我们一直在探索1-氮杂-2-偶氮烯阳离子在分子内反应中的应用，作为一种制备各种氮杂杂环的方法。在这里，我们报道了我们的发现，芳基-1-氮杂-2-偶氮烯阳离子可以通过前所未有的分子内[4+2]环加成反应与侧链烯烃反应，其中偶氮键和一个芳香π键组成4个π组分。1-氮杂-2-偶氮烯阳离子通过几种不同的途径反应，从而产生各种产物。例如，这些物种可以在碳原子上加成亲核试剂来提供偶氮产物，[8]可以进行3，3-Sigmatrotic重排，[9]可以立体专一性地反应
Polar cycloadditions, in which one of the reacting partners is ionic, are less common than cycloadditions involving uncharged or dipolar components, but often occur more readily.[1] For example, whereas [4+ 2] cycloaddition reactions that involve styrene subunits as the 4π component generally require reactive dienophiles or harsh reaction conditions to proceed,[2] the Povarov reaction, which is the stepwise [3][4È+ 2] cycloaddition of N-aryliminium ions with electronrich olefins, occurs readily at or below room temperature.[4, 5] The charge that is present in the ionic partner of polar cycloadditions is often due to the presence of a heteroatom and these systems can provide useful routes to heterocyclic products,[1a] which are prevalent scaffolds in biologically active molecules.[6] Although uncharged heteroallenes have been used extensively in the preparation of heterocyclic compounds,[7] cationic heteroallenes have received less attention. To this end, we have been exploring the use of 1-aza-2-azoniaallene cations (eg 2, Scheme1) in intramolecular reactions as a means of preparing a variety of aza-heterocycles. Herein we report our discovery that aryl-1-aza-2-azoniaallene cations can react by an unprecedented intramolecular [4È+ 2] cycloaddition with pendant alkenes wherein the azo bond and one aromatic π bond make up the 4π component.1-Aza-2-azoniaallene cations are known to react by several different pathways, thus leading to a variety of products. For example, these species can add nucleophiles at the carbon atom to provide azo products,[8] can undergo 3, 3-sigmatropic rearrangements,[9] and can react in stereospecific