Stereoselective [4+2]-Cycloaddition with Chiral Alkenylboranes.
Dongshun Ni1, Brittany P Witherspoon2, Hong Zhang3,4
1Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, IN, 47401, USA.
Angewandte Chemie (International Ed. in English)
|May 12, 2020
Summary
This study introduces a novel stereoselective [4+2]-cycloaddition method using chiral alkenyl oxazaborolidines. The reaction offers a versatile route to complex molecules via C-B bond transformations, with counterions influencing selectivity.
Area of Science:
- Organic Chemistry
- Asymmetric Synthesis
- Organoboron Chemistry
Background:
- Stereoselective cycloadditions are crucial for synthesizing complex organic molecules.
- Alkenylboranes offer unique reactivity but controlling their stereochemistry in cycloadditions remains challenging.
Purpose of the Study:
- To develop a novel method for the stereoselective [4+2]-cycloaddition of alkenylboranes and dienes.
- To utilize chiral N-protonated alkenyl oxazaborolidines as effective dieneophiles in cycloaddition reactions.
Main Methods:
- Employing chiral N-protonated alkenyl oxazaborolidines as dieneophiles in [4+2]-cycloaddition reactions with dienes.
- Utilizing computational evaluation to understand the reaction mechanism and factors influencing stereoselectivity.
Main Results:
- Successful stereoselective [4+2]-cycloaddition of alkenylboranes and dienes was achieved.
- The resulting products can be readily transformed into more complex structures via stereospecific C-B bond manipulations (e.g., oxidation, homologation).
- Computational studies revealed a significant and unexpected influence of the counterion on the reaction's stereoselectivity.
Conclusions:
- A new, effective strategy for stereoselective alkenylborane cycloadditions has been established.
- The developed method provides access to versatile intermediates for organic synthesis.
- Understanding the role of counterions is key for optimizing stereochemical outcomes in such reactions.
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