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The isomerization of allylrhodium intermediates in the rhodium-catalyzed nucleophilic allylation of cyclic imines.

Hepburn HB, Lam HW - Angew. Chem. Int. Ed. Engl. (2014)

Bottom Line: Allylrhodium species generated from potassium allyltrifluoroborates can undergo isomerization by 1,4-rhodium(I) migration to give more complex isomers, which then react with cyclic imines to provide products with up to three new stereochemical elements.High enantioselectivities are obtained using chiral diene-rhodium complexes.

View Article: PubMed Central - PubMed

Affiliation: EaStCHEM, School of Chemistry, University of Edinburgh, Joseph Black Building, The King's Buildings, West Mains Road, Edinburgh, EH9 3JJ (UK) http://www.nottingham.ac.uk/∼pczhl; School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD (UK).

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The isomerization of the allylrhodium species 13.
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fig05: The isomerization of the allylrhodium species 13.

Mentions: The formation of products 12 can be rationalized by the pathway shown in Scheme 5. After formation of the allylrhodium species 13, the imine allylation is disfavored due to the high steric congestion at the γ-carbon. Therefore, 1,4-RhI migration of 13 occurs to form the benzylrhodium species 14. Although the imine can react with 14 at this stage, the observed product is consistent with an allylation by the allylrhodium species 15, formed from 14 by 1,3-allylic transposition of rhodium (through σ–π–σ interconversion). Interestingly, if a cyclic six-membered transition state is operative, the Z-geometry of the alkene in 12 must arise from the methyl group occupying a pseudoaxial position (as in 16), which avoids an unfavorable steric interaction with the cyclooctadiene ligand.


The isomerization of allylrhodium intermediates in the rhodium-catalyzed nucleophilic allylation of cyclic imines.

Hepburn HB, Lam HW - Angew. Chem. Int. Ed. Engl. (2014)

The isomerization of the allylrhodium species 13.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4497600&req=5

fig05: The isomerization of the allylrhodium species 13.
Mentions: The formation of products 12 can be rationalized by the pathway shown in Scheme 5. After formation of the allylrhodium species 13, the imine allylation is disfavored due to the high steric congestion at the γ-carbon. Therefore, 1,4-RhI migration of 13 occurs to form the benzylrhodium species 14. Although the imine can react with 14 at this stage, the observed product is consistent with an allylation by the allylrhodium species 15, formed from 14 by 1,3-allylic transposition of rhodium (through σ–π–σ interconversion). Interestingly, if a cyclic six-membered transition state is operative, the Z-geometry of the alkene in 12 must arise from the methyl group occupying a pseudoaxial position (as in 16), which avoids an unfavorable steric interaction with the cyclooctadiene ligand.

Bottom Line: Allylrhodium species generated from potassium allyltrifluoroborates can undergo isomerization by 1,4-rhodium(I) migration to give more complex isomers, which then react with cyclic imines to provide products with up to three new stereochemical elements.High enantioselectivities are obtained using chiral diene-rhodium complexes.

View Article: PubMed Central - PubMed

Affiliation: EaStCHEM, School of Chemistry, University of Edinburgh, Joseph Black Building, The King's Buildings, West Mains Road, Edinburgh, EH9 3JJ (UK) http://www.nottingham.ac.uk/∼pczhl; School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD (UK).

Show MeSH