Intramolekulare Inversionssubstitution am Dreiring von 77exo-Brombicyclo[4.1.0]heptan-3endo-ol unter Bildung eines Tetrahydrofuranringes
✍ Scribed by Dieter Seebach; Helmut Neumann; Reinhard Dammann
- Publisher
- John Wiley and Sons
- Year
- 1979
- Tongue
- German
- Weight
- 545 KB
- Volume
- 62
- Category
- Article
- ISSN
- 0018-019X
No coin nor oath required. For personal study only.
✦ Synopsis
Intramolecular Substitution under Inversion at the Threemembered Ring of 7__exo__‐Bromobicyclo[4.1.0]heptan‐3__endo__‐ol yielding a Tetrahydrofuran Ring
The reaction 1a → 2a involving substitution at a cyclopropane carbon atom can be observed only with the bromophilic alkyllithium reagents but not with the bases lithium diisopropyl amide (LDA) (Table 1) or potassium t‐butoxide (KTB). The mechanism must be an insertion as outlined in Scheme 1. ‐ The monobromides 1b, 1c and 1d are prepared stereoselectively from the acetal 3a. Again, cyclization of 1b takes only place with LDA in the presence of alkyllithium (Table 2, entries 1‐‐4) suggesting an insertion mechanism (route (a) or (b) in Scheme 2). In contrast, KTB effects the substitution in high yield with no loss (from 1c) or incorporation of deuterium at the cyclopropane substitution center (Table 2, entries 5‐‐7); the possibility is discussed that this process is an S~N~2‐type reaction.