Abstract
Comparison of the cyclisation regiochemistries in the heterolysis and the copper-catalysed homolysis of methyl (E)-3-(2-diazoniophenyl)-2-(3-halophenyl)propenoate tetrafluoroborates indicates that the homolytic pathway involves direct closure of the six-membered ring and not a five-membered ring closure followed by ring expansion. From competition experiments in which homolytic cyclisation of the corresponding non-halogenated compound was run against hydrogen abstraction from hypophosphorous acid, a cyclisation rate constant k(C) = (3.0 +/- 0.5) x 10(9) s(-1) at ambient temperature was estimated which, when used in conjunction with a literature value for the homolytic phenylation of benzene, allows evaluation of a statistically corrected effective molarity of 2 x 10(4) mol dm(-3) for homolytic Pschorr phenanthrene closure. Regioselectivity considerations imply that, by contrast, heterolytic Pschorr phenanthrene closure exhibits unit effective molarity. A mechanistic rationale is presented to explain these patterns of behaviour.
| Original language | English |
|---|---|
| Pages (from-to) | 49-63 |
| Number of pages | 15 |
| Journal | JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2 |
| Issue number | 1 |
| Publication status | Published - Jan 1999 |
Keywords
- ABSOLUTE RATE CONSTANTS
- RING-CLOSURE
- PHENYL RADICALS
- ARYL RADICALS
- WATER LIGANDS
- MASS-SPECTRA
- CIS-STILBENE
- CU-II
- PHOTOCHEMISTRY
- CYCLIZATION