title: An alkene-promoted borane-catalyzed highly stereoselective hydrogenation of alkynes to give Z- and E-alkenes.
abstract: 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(C6 F5 )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.
authors.affiliation: Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (P. R. China), Fax: (+86) 10-62554449.
authors.forename: Yongbing
authors.initials: Y
authors.lastname: Liu
authors.forename: Lianrui
authors.initials: L
authors.lastname: Hu
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.forename: Haifeng
authors.initials: H
authors.lastname: Du
keywords: alkene; alkyne; hydrogenation; metal-free catalysis; stereoselectivity