1H-NMR Spectra of Cyclohexa-1,4-dienes and Cyclohexenes Annellated to Bicyclo[2.2.1]hept-2-enes. The Inter-Ring Homoallylic H,H Coupling Constants as Stereochemical Probes
✍ Scribed by Cyril Mahaim; Pierre-Alain Carrupt; Pierre Vogel
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- German
- Weight
- 792 KB
- Volume
- 68
- Category
- Article
- ISSN
- 0018-019X
No coin nor oath required. For personal study only.
✦ Synopsis
In the course of our studies on the synthesis of anthracyclines [I-41 based on the Diels-Alder additions of exocyclic s-cis-butadiene moieties grafted onto 7-oxabicyclo[2.2. Ilheptane derivatives 1, we observed 'H-NMR spectra of the corresponding adducts 2 with measurable homoallylic 'J(H,H) coupling constants of ca. 1 Hz between the bridgehead protons of the 7-oxabicyclo[2.2. llheptene systems and the allylic protons of the annellated cyclohexene moieties [3-51. This was true for the exo-protons only; no such long-range coupling could be detected for the endo-allylic protons. In order to determine whether this feature could be taken as a probe for the configuration of the Diels-Alder adducts 2, we prepared a series of cyclohexenes and cyclohexa-1,Cdienes annellated to various bicyclo[2.2.l]hept-2-ene and 7-oxabicyclo[2.2.l]hept-2-ene skeletons. We report now on their high-field (360 MHz) 'H-NMR properties and show that the inter-ring homoallylic 'J(H,H) coupling constants indeed constitute the probe we were looking for.