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. 2016 Jan 18;55(3):1108-12.
doi: 10.1002/anie.201508964. Epub 2015 Dec 3.

Chain Walking of Allylrhodium Species Towards Esters During Rhodium-Catalyzed Nucleophilic Allylations of Imines

Jose I Martínez  1 , Joshua J Smith  1 , Hamish B Hepburn  1 , Hon Wai Lam  2
Affiliations

Chain Walking of Allylrhodium Species Towards Esters During Rhodium-Catalyzed Nucleophilic Allylations of Imines

Jose I Martínez et al. Angew Chem Int Ed Engl. .

Abstract

Allylrhodium species derived from δ-trifluoroboryl β,γ-unsaturated esters undergo chain walking towards the ester moiety. The resulting allylrhodium species react with imines to give products containing two new stereocenters and a Z-alkene. By using a chiral diene ligand, products can be obtained with high enantioselectivities, where a pronounced matched/mismatched effect with the chirality of the allyltrifluoroborate is evident.

Keywords: allyltrifluoroborates; asymmetric catalysis; imines; isomerization; rhodium.

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Figures

Scheme 1
Scheme 1
Discovery of allylrhodium chain walking.
Scheme 2
Scheme 2
Effect of geometrical and positional isomerism of the allyltrifluoroborate.
Scheme 3
Scheme 3
Investigation of absolute stereochemical transfer with (R)‐2 a.
Scheme 4
Scheme 4
Enantioselective allylations. Reactions were conducted using 0.30 mmol of 1 b. The diastereomeric ratios were confirmed by 1H NMR analysis of the unpurified reactions. Yields are of isolated products. Enantiomeric excesses were determined by HPLC analysis on a chiral stationary phase. [a] Using 2.5 equivalents of allyltrifluoroborate 2 g.
Scheme 5
Scheme 5
Investigation of matched/mismatched effects.
Scheme 6
Scheme 6
Proposed catalytic cycle.
Scheme 7
Scheme 7
Rationale for the formation of crossover product 3 a.
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References

    1. For chain walking polymerization, see:
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    1. For a review of catalytic alkene isomerization-hydroformylation reactions, see: Vilches-Herrera M., Domke L., Börner A., ACS Catal. 2014, 4, 1706–1724.

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