Ouroboros: Heterocycles closed by dative σ bonds and stabilized by π delocalization
2018; Elsevier BV; Volume: 75; Issue: 3 Linguagem: Inglês
10.1016/j.tet.2018.11.058
ISSN1464-5416
AutoresKelling J. Donald, Samuel Gillespie, Ziad Shafi,
Tópico(s)Radical Photochemical Reactions
ResumoHeteroarenes 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′(CH2)mD′ and A′(CH)mD′, 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.
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