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Issue 23, 2003
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On benzo[b][1,4]diazepinium-olates, -thiolates and -carboxylates as anti-Hückel mesomeric betaines

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2,3-Diaminophenol 4, 3,4-diaminophenol 5, 4-methoxy-1,2-diaminobenzene 6, 3,4-diaminobenzenethiol 7, 2,3-diaminobenzoic acid 8, and 3,4-diaminobenzoic acid 9 were reacted with 2,4-pentanedione to yield the corresponding benzo[b][1,4]diazepinium salts, respectively. The hydroxy-benzo[b][1,4]diazepinium salts 17 and 18 do not form mesomeric betaines (MB) on deprotonation. Instead, they are converted into the diimines 24 and 25. By contrast, the 7-mercaptobenzo[b][1,4]diazepinium salt 20 yields the corresponding thiolate on increasing the pH of the solution. This MB, which possesses 4n π-electrons, does not fit into the classification system of heterocyclic mesomeric betaines accepted today. Deprotonation of the betaine results in the formation of an instable anionic thiolate 31 which oxidizes immediately to the disulfide 32. The carboxy derivatives 21 and 22 readily form cross-conjugated mesomeric betaines. Whereas the diimine 34 proved to be instable, the sodium salt of the diimine 36 was unambiguously characterized. An X-ray single crystal analysis of 22 as its picrate is presented in order to gain additional insights into these 4n π-electron systems.

Graphical abstract: On benzo[b][1,4]diazepinium-olates, -thiolates and -carboxylates as anti-Hückel mesomeric betaines

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The article was received on 23 Jul 2003, accepted on 26 Sep 2003 and first published on 20 Oct 2003

Article type: Paper
DOI: 10.1039/B308412D
Citation: Org. Biomol. Chem., 2003,1, 4342-4350

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    On benzo[b][1,4]diazepinium-olates, -thiolates and -carboxylates as anti-Hückel mesomeric betaines

    A. Schmidt, A. G. Shilabin and M. Nieger, Org. Biomol. Chem., 2003, 1, 4342
    DOI: 10.1039/B308412D

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