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Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
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Which NICS aromaticity index for planar pi rings is best?

Hossein Fallah-Bagher-Shaidaei1, Chaitanya S Wannere, Clémence Corminboeuf

  • 1Department of Chemistry, Islamic Azad University-Rasht Branch, P.O. Box 41335-3516, Rasht, Iran. h_fallah@iaurasht.ac.ir

Organic Letters
|February 24, 2006
PubMed

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Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
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The basicity of aromatic amines is much weaker than that of aliphatic amines due to the involvement of the lone pair of electrons over the N atom in resonance with the aryl rings. Generally, the electron-donating ability of any substituents on the aryl ring of aromatic amines increases the basicity of the amine by increasing electron density, and hence the availability of lone pair on the nitrogen. On the other hand, electron-withdrawing functional groups on the aryl ring of amines decrease the...
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