2-卤代-N-吡啶基苯甲酰胺的光反应：苯基自由基的分子内环化机理与氯自由基的n-络合。,The Journal of Organic Chemistry

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2-卤代-N-吡啶基苯甲酰胺的光反应：苯基自由基的分子内环化机理与氯自由基的n-络合。
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2001-04-03 , DOI: 10.1021/jo001470e
Y T Park ₁ , C H Jung , M S Kim , K W Kim , N W Song , D Kim

Affiliation

研究了2-卤代-N-吡啶基苯甲酰胺（图1中的1-4）的光化学行为。2-氯-N-吡啶基苯甲酰胺1a，2a，3a和4的光反应可提供高收率的光环化产物苯并[c]萘啶酮（6-9和16），而溴代类似物1b，2b和3b产生大量光还原的产品，N-吡啶基苯甲酰胺（1c，10和11），以及次要的光环化产品。由于2-氯-N-吡啶基苯甲酰胺的光环化反应由于氧气的存在而被阻滞，并且由于三重态敏化剂，丙酮或苯乙酮的存在而被敏化，因此氯类似物的三重态处于反应中。由于在2-氯-N-吡啶基苯甲酰胺的激光闪光光解中发现了几种自由基中间体，尤其是氯自由基的n-络合物，提出了苯基自由基与氯自由基的n-络合辅助的分子内环化机理，以用于环化反应：由1a激发而形成的氯代类似物（1a）的三重态（78 kcal / mol）经历均相裂解C-Cl键以产生苯基和氯基；当氯自由基通过n络合物保持相邻的吡啶基环时，苯基与吡啶基环的分子内芳基化反应产生共轭的2,3-二氢吡啶基自由基，然后该共轭自由基芳构化，得到环化产物苯并[通过喷出氢使萘啶酮。光还原产物可以通过从环境中夺取苯基sigma自由基的氢原子来形成。

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Photoreaction of 2-halo-N-pyridinylbenzamide: intramolecular cyclization mechanism of phenyl radical assisted with n-complexation of chlorine radical.

The photochemical behavior of 2-halo-N-pyridinylbenzamide (1-4 in Chart 1) was studied. The photoreaction of 2-chloro-N-pyridinylbenzamides 1a, 2a, 3a, and 4 afforded photocyclized products, benzo[c]naphthyridinones (6-9 and 16), in high yield, whereas the bromo analogues 1b, 2b, and 3b produced extensively photoreduced products, N-pyridinylbenzamides (1c, 10, and 11), with minor photocyclized product. Since the photocyclization reaction of 2-chloro-N-pyridinylbenzamide is retarded by the presence of oxygen and sensitized by the presence of a triplet sensitizer, acetone or acetophenone, a triplet state of the chloro analogue is involved in the reaction. Since several radical intermediates, particularly n-complexes of chlorine radical, are identified in the laser flash photolysis of 2-chloro-N-pyridinylbenzamide, an intramolecular cyclization mechanism of phenyl radical assisted with n-complexation of chlorine radical for the cyclization reaction is proposed: the triplet state (78 kcal/mol) of the chloro analogue (1a), which is populated by the excitation of 1a undergoes a homolytic cleavage of the C-Cl bond to give phenyl and chlorine radicals; while chlorine radical holds the neighbor pyridinyl ring with its n-complexation, the intramolecular arylation of the phenyl radical with the pyridinyl ring proceeds to produce a conjugated 2,3-dihydropyridinyl radical and then the conjugated radical aromatizes to afford a cyclized product, benzo[c]naphthyridinone by ejecting a hydrogen. The photoreduction product can be formed by hydrogen atom abstraction of the phenyl sigma radical from the environment.

更新日期：2019-11-01

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