20657-30-1Relevant academic research and scientific papers
An alkene-promoted borane-catalyzed highly stereoselective hydrogenation of alkynes to give Z- And E-alkenes
Liu, Yongbing,Hu, Lianrui,Chen, Hui,Du, Haifeng
, p. 3495 - 3501 (2015)
The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Zalkenes, 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.
sym-1,2-Diarylethylenes from α-Lithiated Benzylic Sulfones. Catalysis by Elemental Tellurium
Engman, Lars
, p. 3559 - 3563 (2007/10/02)
The stability of α-lithiated alkyl, allyl, and benzyl phenyl sulfones was studied. α-Lithiated benzyl phenyl sulfones were found to give sym-1,2-diarylethylenes slowly when kept in tetrahydrofuran at ambient temperature for several days.The reaction time was significantly reduced if a catalytic amount (18-24percent) of elemental tellurium was present in the reaction.Other chalcogenides were less effective in this respect.The uncatalyzed reaction produced essentially pure trans olefins whereas the tellurium-catalyzed process afforded substantial amounts of cis isomer(usually 15-35percent).Tellurium tetrachloride in chloroform at ambient to reflux temperature was found to be highly effective in promoting cis/trans isomerization of 1,2-diarylethylenes.The involvement of a carbene mechanism or an intermolecular reaction of α-lithiated benzyl phenyl sulfones is considered in a mechanistic discussion.
