The Most Stable and Fully Characterized Functionalized Heptacene
The Most Stable and Fully Characterized Functionalized Heptacene
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DOI：
10.1002/anie.200803345
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Wudl, Fred
中科院分区：
文献类型：
--
作者：
Chun, Doris;Cheng, Yang;Wudl, Fred
理论计算预测并苯家族中的带隙能量随着每个连续的苯环加成至并六苯而变窄，超过该带隙，HOMO-LUMO（HOMO=最高占据分子轨道，LUMO=最低未占据分子轨道）带隙保持恒定，因为在基态中出现了单线态双自由基特征。[4，5]因此，长并苯的电子性质长期以来一直是争论的主题。[6]虽然较小的线性多环芳烃（2与n 5）的物理性质得到了很好的探索，我们的知识较长的并苯是有限的两个主要原因：1）在其生产和不溶性的合成挑战和2）他们的极端不稳定性与长度增加，这使得他们的特征只能通过电子光谱在一个矩阵在低温下。Neckers及其同事报告了在PMMA基质中光化学生成的并六苯和并七苯的稳定性研究。[7，8]然而，这些分子不能被分离，当被聚合物基质保护时，它们仅稳定几个小时。[7，8] Anthony及其同事证明了一种稳定和增溶长PAH的有效方法，他们策略性地用烷基甲硅烷基乙炔基官能化并苯主链。[9]官能化多并苯的最常见的合成路线是通过有机金属试剂与并苯醌的亲核加成，然后还原得到所需产物。[10-15]我们探索了其他方法来提供官能化高级并苯的新途径。据我们所知，本文报道的工作是第一个报道的双Diels-Alder环加成之间的横向“双蒽”和二烯，然后还原，得到七并苯衍生物1a-c将2，5-二芳基-6-氧代-1，3，4-恶二嗪-6-酮3 [16]是一种缺电子二烯，其经历逆需电子狄尔斯-与苯炔进行两次桤木反应，得到所得蒽衍生物4。[17]用二苯基异苯并呋喃捕获“双蒽”（通过二溴化物4的顺序脱卤化氢产生），得到双内氧化物5。5的金属还原提供了预期的官能化七并苯1a、B（方案2）。
Theoretical calculations predict a narrowing of band gap energies in the acene family with each successive benzene ring addition up to hexacene, beyond which the HOMO–LUMO (HOMO= highest occupied molecular orbital, LUMO= lowest unoccupied molecular orbital) gap remains constant because of the emergence of a singlet biradical character in the ground state.[4, 5] Hence, the electronic properties of the longer acenes have long been a subject of debate.[6] While the physical properties of the smaller linear PAHs (2 with n 5) are well explored, our knowledge of longer acenes is limited for two major reasons: 1) the synthetic challenge in their production and their insolubility and 2) their extreme instability with increased length, which makes them characterizable only by electronic spectroscopy in a matrix at low temperatures. Neckers and co-workers have reported stability studies of hexacene and heptacene generated photochemically in PMMA matrix.[7, 8] However, these molecules could not be isolated and they are stable for only a few hours when protected by the polymer matrix.[7, 8] An effective approach to stabilize and solubilize long PAHs was demonstrated by Anthony and co-workers who strategically functionalized the acene backbone with alkylsilylethynyl groups.[9] The most common synthetic route to functionalized polyacenes is through the nucleophilic addition of organometallic reagents to an acene quinone, followed by reduction to afford the desired product.[10–15] We explored other methodologies to provide a new route to functionalized higher acenes. To the best of our knowledge, the work reported herein is the first report of a double Diels–Alder cycloaddition between a lateral “bisanthracyne” and dienes, followed by reduction to give heptacene derivatives 1a–c (Scheme 1).The 2, 5-diaryl-6-oxo-1, 3, 4-oxadiazine-6-one 3 [16] is an electron-deficient diene that undergoes an inverse-electrondemand Diels–Alder reaction twice with benzyne to give the resulting anthracene derivative 4.[17] Trapping of the “bisanthracyne”(generated through sequential dehydrohalogenation of dibromide 4) with diphenylisobenzofuran afforded bisendo-oxide 5. Metal reduction of 5 provided the expected functionalized heptacenes 1a, b (Scheme 2).