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Isopinocampheylborane derivatives with >99% ee via the DMAP complex
1Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
The Journal of Organic Chemistry
|August 12, 2006
Summary
Chiral isopinocampheylborane complexes are synthesized with high enantiomeric excess (>99% ee) from alpha-pinene via hydroboration. These stable intermediates allow for further transformations without significant loss of chirality.
Area of Science:
- Organoborane Chemistry
- Asymmetric Synthesis
- Chiral Reagents
Background:
- Alpha-pinene is a readily available chiral terpene.
- Isopinocampheylborane derivatives are valuable chiral auxiliaries.
- Efficient synthesis of enantiomerically pure boranes is crucial for asymmetric synthesis.
Purpose of the Study:
- To develop a highly enantioselective synthesis of isopinocampheylborane-DMAP complex.
- To investigate the stability and purification of the synthesized complex.
- To evaluate the retention of enantiomeric excess during subsequent transformations.
Main Methods:
- Hydroboration of alpha-pinene using DMAP.BH3 activated by iodine.
- Conventional hydroboration of alpha-pinene followed by DMAP addition.
- Crystallization for purification and conversion to trifluoroborate and other derivatives.
Main Results:
- Isopinocampheylborane-DMAP complex (8) obtained with >99% enantiomeric excess (ee).
- Purification by methanol crystallization yields an air-stable complex.
- Subsequent conversions to trifluoroborate adduct (1) and other derivatives show minimal ee loss.
Conclusions:
- A robust and highly enantioselective method for preparing isopinocampheylborane-DMAP complex is established.
- The complex is stable and readily purified, facilitating its use as a chiral reagent.
- The synthetic route preserves high enantiomeric purity throughout subsequent derivatization steps.