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行政院國家科學委員會專題研究計劃結案報告
光 與 熱 化 學 產 生 的 自 由 基 對 與 雙 自 由 基 之 研 究
The Studies of Photo- and Thermo-generated Radical Pairs and
Biradicals
計劃編號：NSC 91-2113-M-009-017 執行期限：91 年 8 月 1 日至 92 年 7 月 31 日 主持人：鍾文聖 國立交通大學應化系 wschung@cc.nctu.edu.tw 一、中文摘要 我們完成了 alpha 芳基塞吩、砒咯類 sultines 化合物以及 disultines 的合成，這些 化合物可以是雙自由基、自由基對或四自 由基的前驅物，其構造如計畫書中所示。 在成功合成這些化合物之後，除了與 王念夏及陳益佳兩教授合作，進行雷射瞬 態吸收光譜及反應動力學之研究之外，也 針對上述的各種 sultines 進行光化學反 應，並利用自由基捕捉試劑（各式烯類及 捕捉後能產生安定自由基的試劑 MNP, DMPO），希望能釐清究竟反應中間體是 自由基對或雙自由基。除了產物的分析與 鑑定，此類化合物的電子順磁共振光譜 (ESR)以及低溫介質霍氏紅外光譜的量 測，提供了自由基極為寶貴的資訊。 當上述的 sultines 與 C60進行高溫迴 流，很容易脫去 SO2產生活性極高的雜環 o-quinodimethanes，反應得到立體專一性的 1:1 Diels-Alder 加成產物，產率約 53~84%。 變溫的碳核磁共振光譜亦支持上述的碳六 十加成產物之構造，同時提供光譜與對稱 性之關聯性的重要佐證。 過去這一年我們合成了一系列 2,5-雙 芳基砒咯雙自由基前驅物以及進行其光解 與熱解實驗。由這些化合物與控制實驗我 們首次獲得參態雙自由基的電子自旋共振 光譜，與耶魯的 Berson 教授在 1997 年所 發表的三篇 JACS 系列文章相符，然而我 們的重大發現獲致不同的結論。 關鍵詞：雜環鄰菎二烯、自由基對、雙自 由基、2,5-雙芳基砒咯、電子自旋共振光 譜、霍氏紅外光譜。 AbstractWe have completed the syntheses of several α,α−disubstituted thienosultines, pyrrolosultines, and disultines. These sultines are precursors for radical pairs, biradicals or tetraradicals, as shown in our proposals of 2002.
After successfully synthesizing these compounds, we not only collaborate with Professors N.-S. Wang and I.-Chia Chen to study their transient absorption spectroscopy and kinetics but also study the steady state photochemistry of these sultines in the presence and absence of radical trapping reagents (such as various olefins and MNP, DMPO etc.). We hope, through this work, one may gain strong insights on the involvement of radical pairs or biradicals in the photolysis. Besides traditional product separation and analysis, we also focused on the ESR and Matrix Isolated FTIR of these molecules, which provides valuable information about the reactive radical intermediates.
When heated in the presence of [60]fullerene, the sultines all underwent extrusion of SO2 and the resulting
2 heterocyclic-o-quinodimethanes were trapped as the 1:1 adducts in 53% to 84% yields. Various temperature 13C-NMR spectroscopy also provides important information about the structure of cycloadducts and reveals interesting spectra and symmetry relationship.
In the past year, we studied the thermolysis and photolysis of a series of 2,5-diaryl-substituted N-tosylpyrroles and for the first time, we were able to obtain triplet EPR spectra of these species. The EPR spectra of these sultines and the parent compounds (without the sultine functional groups) reproduced the EPR spectra by J. A. Berson in three JACS papers published in 1997, however, different conclusions are reached from our results!
Keywords: o-quinodimethanes, Radical Pairs,
Biradicals 2,5-diarylpyrroles, Electron Spin Resonance Spectroscopy, FTIR.
二、緣由與目的 雖然鄰菎二烯 1 已經廣泛被使用於製 備碳六十的衍生物，但是雜環鄰菎二烯之 重要性，直到最近才獲得相當的重視。目 前已有許多產生此類高活性鄰菎二烯的方 法，其中以從雜環駢 3-sulfolenes 脫去 SO2 的方法最常見。Quinoxalines 類化合物是天 然物中存在的芳香雜環，他們通常具有生 物活性及醫藥性質，因此找出一種容易合 成且高產率生成雜環 quinoxalino-o-quino- dimethanes 的方法，便成為研究上重要的課 題。
Although o-quinodimethane 1 has been frequently been used for the derivatization of [60]fullerene, their heterocyclic analogues have been recognized only recently. Various methods for generating these highly reactive diene have been developed. Among them cheletropic elimination of SO2 from hetero-aromatic-fused 3-sulfolenes has drawn the most attention. Quinoxalines are important naturally occurring heterocycles and are usually
found to have biological and pharmaceutical activity. Finding an easy, high yield method for generating quinoxalino-o-quinodimethanes is thus of particular interest.
三、結果與討論 將 2,5- 雙取代? 吩sultines與一些典型 的缺電性的親雙烯物反應，sultines會先脫 去SO2的小分子，進而生成non-Kekulé的雙 自由基分子，然後與親雙烯物生成1:1的加 成產物，產率大致在50-85%之間。將Sultines 及sulfolenes與不同濃度的親雙烯物進行高 溫裂解實驗，發現反應可能經由兩種途徑: 其一為起始物與雙自由基中間物先達成平 衡，另一則為Diels-Alder與Retro-Diels-Alder 的反應機制；不過單純由濃度效應無法區 分上述機制何者適用。 將 Sultine 與 正 丁基鋰試劑反應發生親核性開環反應，經 由水的處理之後得到亞? 醇產物。另外， 將 Sultine 5a 與 甲 醇 、 含 氘 取 代 甲 醇 (methanol-d4)、2-硫醇基乙醇等試劑一起在 苯溶液中封管加熱，可以獲得約1:1的捕捉 產 物 19-21 與重排產物sulfolene 6a。產物 19-21的獲得，可以藉由加熱之後產生雙自 由基或是離子中間物來解釋。(詳細結果請 參 考 著 作 : J. Org. Chem. 2002, 67, 9267-9275.) 將碳六十與微過量的2,5-雙取代? 吩 sultines在 鄰 二 氯 苯 中 加 熱 迴流，不同的 sultines其加熱時間不同，可以分別獲得碳 六十的1:1加成產物，產率大約在53-84%之 間 。 這 與 之 前 本 實 驗 室 研 究 quinoxaline sultines之結果相似，請參考拙著: J. Org. Chem. 2000, 65, 3395。 2,5-disubstituted-thienosultines(5,7- disubstituted-1,4-dihydro-1H-3λ4-thieno- [3,4-d][2,3]oxathiin-3-oxides) 5a-d, are prepared from the corresponding dichlorides
4a-d with commercially available Rongalite
(sodium formaldehyde sulfoxylate) reagent in 17~60% yields. When heated in the presence of electron-poor dienophiles, sultines 5a-d
3 underwent elimination of SO2, and the resulting non-Kekulé biradicals 7a-d were intercepted as the 1:1 adducts (8-12) in good to excellent yields. The pyrolysis of sultines and sulfolenes with different concentration of dienophiles revealed that either a pre-equilibrium between starting reagents and biradical species or a Diels-Alder and retro-Diels-Alder reaction mechanisms may be involved, however, more work is necessary to establish the proposed mechanisms.
Reaction of sultine 5b with nBuLi was found to undergo a nucleophilic ring-opening reaction to give sulfinyl alcohol 17 after H2O work up. When sultine 5a was heated in benzene in a sealed tube in the presence of methanol, methanol-d4, or 2-mercaptoethanol, the respective 1:1 trapping adducts 19-21 as well as the rearranged sulfolene 6a were isolated in similar amounts. The isolation of adducts 19-21 may be explained by the involvement of either biradical or ionic intermediates during the pyrolysis. (For details about this work, please refer to J. Org. Chem.
2002, 67, 9267-75).
When C60 was refluxed in
o-dichlorobenzene for a variable period of time
with a slight excess of the 2,5-disubstituted thienosultines 5a-d, the 1:1 cycloadducts were obtained in 53-84% yield. The results with [60]fullerene are similar to those observed for quinoxalino-sultines. For details, please refer to our previous work: J. Org. Chem. 2000,
65, 3395.
四、計劃成果自評
本計劃大部份依原定計劃如期完成， 已 經 發 表 論 文 篇 如 下 ： (1) J. Chinese.
Chem. Soc. 2002, 49, 77；(2) J. Org. Chem.
2002, 67, 9267-75。另外與王念夏教授及陳 益佳教授合作部分，也經由雷射瞬態光解 偵測到自由基及活性中間體的光譜，並經 由與烯類進行的反應動力學，獲得很多有 關自由基反應速率的珍貴資料，我們已著 手進行整理，有兩篇投稿送審之中。 另外與王念夏教授及陳益佳教授合作部 分，也經由雷射瞬態光解偵測到自由基及 活性中間體的光譜，並經由與烯類進行的 反應動力學，獲得很多有關自由基反應速 率的珍貴資料，我們已著手進行整理，有 兩篇投稿送審之中。
Most of the proposed work are successfully carried out and two papers have been published in related subjects: (1) J.
Chinese. Chem. Soc. 2002, 49, 77；(2) J. Org. Chem. 2002, 67, 9267-75. The collaboration
work with Prof. Wang and Chen, which is related to laser flash photolysis and kinetics, provides us useful information about the reactive intermediates. Based on the work, two manuscripts have been submitted.
