1. Ouroboros: Heterocycles closed by dative σ bonds and stabilized by π delocalization.
- Author
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Donald, Kelling J., Gillespie, Samuel, and Shafi, Ziad
- Subjects
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COORDINATE covalent bond , *HETEROCYCLIC compounds , *HETEROARENES , *CHEMICAL bonds , *ISOMERS , *BENZENE - Abstract
Abstract Heteroarenes such as (aza and oxa)borines are increasingly important as synthetic targets and reagents. We map the intramolecular cyclization of saturated heterocyclic chains through dative bonding. A related set of planar unsaturated aza-, oxa-, and fluora- rings that feature dative σ bonding enhanced by π delocalization are identified. The systems have, in general, the formulae A′(CH 2) m D′ and A′(CH) m D′, where m = 3 and 4, and A′ and D′ are acceptor and donor sites, respectively. In each case, the ring isomers, achievable via A′←D' internal coordination (in the manner of Kekulé's ouroboros), are more stable than chains. Unsaturated aromatic rings examined herein include a oxadiborine with a hypervalent oxygen center and a dioxadiborine. They are isoelectronic with an azaborine, which was synthesized more recently, and benzene. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]
- Published
- 2019
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