FORMATION OF TRIPLET BIRADICALS BY [3+2]-PHOTOCYCLOADDITION OF ARENES WITH ALKENES

芳烃与烯烃的[3 2]-光环加成反应形成三重态双自由基

• 批准号: 11640534
• 负责人: KUBO Yasuo
• 金额: $ 1.6万
• 依托单位: SHIMANE UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640534/
• 关键词: CYCLOADDITIONS; PHOTOCHEMICAL REACTIONS; TRIPLET BIRADICALS; NON-KEKULE STRUCTURE; ESR; ACID DERIVATIVES; ESTERS; NITRILES

The purpose of this investigation is to clarify the features of the formation of triplet biradicals by [3+2]-photocycloaddition of arenes and alkenes.The results obtained are as follows :1. The [3+2]-photocycloaddition of dimethyl 1, 4-naphthalenedicarboxylate (1) and alkenes was found to occur from the singlet excited state of 1 possibly through a zwitter-ionic intermediate. On the other hand, the photoreactions in the presence of a radical scavenger, such as oxygen and fumaronitrile, radical scavengeradded [3+2]-cycloadducts were obtained in concomitant loss of the formation of the [3+2]-cycloadducts. Control examinations indicated that the [3+2]-adducts were not the precursors of the adducts of the radical scavenger. A mechanism on the formation of the adducts, involving a triplet biradical intermediate occurred from the zwitter-ionic intermediate, was proposed. From the investigations of the photoreactions of various arenes and alkenes, the formation of the triplet biradicals was found to be efficient in the photoreactions of aromatic esters and alkenes, having aromatic substituents, such as styrene, in less polar solvents, such as benzene and carbon tetrachloride, at low temperature.2. The corresponding intramolecular photoreactions revealed that the triplet biradicals were also effectively formed in the intramolecular reactions in less polar solvents at low temperature.3. The quenching rate constants of the fluorescence of 1 by the alkenes were measured and a large rate constant was found to be essential for the effective formation of the triplet biradicals. On the other hand, no effective fluorescence quenching was observed in the quenching by the radical scavengers.4. The molecular orbital calculation revealed that the triplet biradicals, obtained by approaching of the alkene units to the 1, 8-position of the naphthalene ring of 1, were more stable (11-18 kcal/mol) than the corresponding singlet zwitter-ionic intermediates.

本研究的目的是阐明芳烃和烯烃的[3+2]-光环加成反应生成三重态双自由基的特征，得到的结果如下：1。发现1，4-萘二甲酸二甲酯（1）与烯烃的[3+2]-光环加成反应可能是从1的单重激发态通过两性离子中间体进行的。另一方面，在自由基清除剂如氧和乙腈的存在下，光反应得到自由基清除剂加成的[3+2]-环加合物，同时失去[3+ 2]-环加合物的形成。对照试验表明，[3+2]-加合物不是自由基清除剂加合物的前体。提出了一种由两性离子中间体生成三重态双自由基中间体的加合物形成机理。通过对各种芳烃和烯烃光反应的研究，发现在低温下，在极性较小的溶剂中，如苯和四氯化碳，具有芳香取代基的芳香酯和烯烃（如苯乙烯）的光反应中，三重态双自由基的形成是有效的.相应的分子内光反应表明，在较低极性溶剂中，低温下的分子内反应也能有效地形成三重态双自由基.测量了烯烃对1荧光的猝灭速率常数，发现一个大的速率常数是有效形成三重态双自由基所必需的。另一方面，自由基清除剂对荧光的猝灭作用不明显.分子轨道计算结果表明，由烯烃单元靠近1萘环的1，8位得到的三重态双自由基比相应的单重态两性离子中间体稳定（11-18 kcal/mol）.