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Stereoselectivity and regioselectivity in the segment-coupling Prins cyclization
J J Jaber1, K Mitsui, S D Rychnovsky
1Department of Chemistry, University of California, Irvine, CA 92697-2025, USA.
The Journal of Organic Chemistry
|June 26, 2001
Summary
This study explores segment-coupling Prins cyclizations for synthesizing tetrahydropyrans. Alkene geometry controls stereochemistry, offering a versatile method for organic synthesis.
Area of Science:
- Organic Chemistry
- Synthetic Methodology
- Stereoselective Synthesis
Background:
- The Prins cyclization is a valuable reaction in organic synthesis.
- Controlling stereochemistry in cyclization reactions is crucial for creating complex molecules.
Purpose of the Study:
- To investigate the scope and limitations of the segment-coupling Prins cyclization.
- To establish the stereoselectivity and regioselectivity of this reaction for tetrahydropyran synthesis.
Main Methods:
- Esterification of homoallylic alcohols followed by reductive acetylation.
- Lewis acid-catalyzed cyclization of alpha-acetoxy ethers.
- Investigation of various dienols and alkene geometries.
Main Results:
- Alkene geometry (E vs. Z) dictates product stereochemistry (equatorial vs. axial substituents).
- Dienols with one allylic and one homoallylic alkene cyclize efficiently.
- Dienols with two homoallylic alkenes show modest to high regioselectivity.
- Relative cyclization rates established: vinyl > Z-alkene > E-alkene > alkyne.
Conclusions:
- The segment-coupling Prins cyclization provides a stereoselective and regioselective route to tetrahydropyrans.
- Product configurations are consistent with cyclization through a chair conformation.
- The 2-oxonia Cope rearrangement may influence regioselectivity and stereoselectivity in diene cyclizations.