Solvent-dependent stereoselectivity in a Still-Wittig rearrangement: an experimental and ab initio study
S A Hart1, C O Trindle, F A Etzkorn
1Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.
Abstract:
[see reaction]. The Still-Wittig rearrangement gave opposite selectivities for (Z:E)-alkenes in THF (3:1) vs toluene (1:3) in the synthesis of serine-proline dipeptide amide isosteres. Four transition states leading to (Z)-and (E)-alkenes with THF and without (representing toluene) were identified by ab initio calculations at the 3-21G* level. The calculated (Z:E)-ratios with THF (4.7:1) and without THF (1:3.2) suggested that the transition state geometries and energies were well-represented by the calculations.
More Related Videos
Related Concept Videos
SN2 Reaction: Stereochemistry
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
Regioselectivity and Stereochemistry of Hydroboration
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement
[3,3] Sigmatropic Rearrangement of Allyl Vinyl Ethers: Claisen Rearrangement


