An Alkene-Promoted Borane-Catalyzed Highly Stereoselective Hydrogenation of Alkynes to Give Z- and E-Alkenes

The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z‐alkenes, the hydrogenation of alkynes to give E‐alkenes is still not well resolved. In particular, selective preparation of both Z‐ an...

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Bibliographic Details
Published in:Chemistry : a European journal 2015-02, Vol.21 (8), p.3495-3501
Main Authors: Liu, Yongbing, Hu, Lianrui, Chen, Hui, Du, Haifeng
Format: Article
Language:English
Subjects:
alkene
Alkenes
alkyne
Alkynes
Boranes
Catalysis
Chemical synthesis
Chemistry
Hydrogenation
Hydrogenolysis
metal-free catalysis
Olefins
Organic chemistry
Stereoselectivity
Strategy
Transformations
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Summary:The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z‐alkenes, the hydrogenation of alkynes to give E‐alkenes is still not well resolved. In particular, selective preparation of both Z‐ and E‐alkenes by the same catalytic hydrogenation system using molecular H2 has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C6F5)2‐catalyzed metal‐free hydrogenation of alkynes was adopted. Significantly, both Z‐ and E‐alkenes can be furnished by hydrogenation with molecular H2 in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H2 play an essential role in promoting the hydrogenolysis reaction. With a little help from an alkene! A HB(C6F5)2‐catalyzed metal‐free hydrogenation of alkynes, promoted by an alkene through HF interactions, was successfully achieved. Z‐ and E‐alkenes can be accessed respectively in high yields with excellent stereoselectivities (see scheme; TS=transition state).
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201405388