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Solvolytic enolization of scytalone
G S Basarab1, D B Jordan, Y J Zheng
1E. I. DuPont de Nemours Central Research and Development, Wilmington, Delaware 19880-0328, USA. gregory.s.basarab@usa.dupont.com
Organic Letters
|June 7, 2000
Summary
Scytalone primarily adopts an envelope conformation, confirmed by quantum mechanics and NMR. Its C2 hydrogen exchange rates and enolate formation mechanisms reveal insights into its chemical reactivity.
Area of Science:
- Organic Chemistry
- Computational Chemistry
- Spectroscopy
Background:
- Scytalone is a key intermediate in fungal melanin biosynthesis.
- Understanding its conformational dynamics is crucial for elucidating its reactivity.
- Previous studies have suggested potential conformations but lacked detailed experimental and computational validation.
Purpose of the Study:
- To determine the major conformation of scytalone.
- To investigate the stereochemical aspects of hydrogen exchange at the C2 position.
- To model the transition state for enolate formation to understand deprotonation pathways.
Main Methods:
- Quantum mechanical calculations were employed to predict conformational preferences.
- Nuclear Magnetic Resonance (NMR) spectroscopy was used to corroborate the determined conformation.
- Transition state modeling was performed to analyze the mechanism of enolate formation.
Main Results:
- The major conformation of scytalone exhibits an envelope shape with the C3 hydroxyl group in an equatorial position.
- The axial pro-R hydrogen at C2 exchanges slower with the solvent compared to the equatorial pro-S hydrogen.
- Enolate formation likely proceeds via a flipped envelope conformation where both the C3-hydroxyl and C2 pro-S hydrogen are axial.
Conclusions:
- Scytalone's conformational flexibility is significant and influences its reactivity.
- The stereochemistry at C2 plays a role in its susceptibility to solvent exchange.
- Deprotonation leading to enolate formation is facilitated by a specific, transient conformation.