452094-47-2Relevant academic research and scientific papers
Can polarization of triple bond in tolanes be deduced from 13C NMR shifts? Re-evaluation of factors affecting regiochemistry of the palladium-catalyzed hydrostannation of alkynes
Rubin, Michael,Trofimov, Alexander,Gevorgyan, Vladimir
, p. 10243 - 10249 (2007/10/03)
Polarization of the triple bond in a series of differently substituted ortho and para-tolanes has been studied by NMR and computational methods in order to examine if 13C NMR data can be effectively used for the assessment of electronic polarization of a triple bond in diarylacetylenes. DFT calculations of both natural charges and NMR properties revealed that chemical shifts concur with effective charges on sp-carbon atoms in para-tolanes, whereas in ortho-analogues magnetic anisotropy complicates the analysis making 13C NMR data inapplicable for ascribing triple bond polarization. The obtained information was used to reevaluate factors affecting the regiochemistry of the Pd-catalyzed hydrostannation of the triple bond in tolanes. Computational study on the polarization of triple bonds taken together with the experimental data on hydrostannation of various mono- and disubstituted tolanes bearing para- and ortho-substituents demonstrated that the regioselectivity of hydrostannation is governed by a combination of electronic and steric factors. In para-tolanes, the electronic effect prevails and α- and β-vinylstannanes are obtained predominantly for substrates with electron-withdrawing and electron-donating groups, respectively. In the ortho-series, steric factors dominate over electronics and α-isomers are produced with high selectivity regardless of the substituents' nature. However, it was found that in disubstituted "push-pull" tolanes steric control of an ortho-group can be overruled by the very strong electronic effect of an electron-withdrawing substituent in para-position.
Ortho substituents direct regioselective addition of tributyltin hydride to unsymmetrical diaryl (or heteroaryl) alkynes: An efficient route to stannylated stilbene derivatives
Alami, Mouad,Liron, Frederic,Gervais, Marina,Peyrat, Jean-Francois,Brion, Jean-Daniel
, p. 1578 - 1580 (2007/10/03)
An unprecedented ortho-directing effect (ODE) in diaryl alkynes 1 (R=electron-withdrawing or electron-donating group) promotes regioselective addition of tributyltin hydride to the triple bond and afforded efficiently stannylated unsymmetrical 1,2-diaryl olefins 2. The precise contributions of steric, electronic, and coordinative factors, which control this regioselectivity are highlighted. The results are rationalized in terms of electronic polarization across the alkyne bond, induced by the ortho substituent whatever its electronic nature.
