- Chemoselective construction of substituted conjugated dienes using an olefin cross-metathesis protocol
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(Chemical Equation Presented) Various substituted conjugated dienes have been made by olefin cross-metathesis. Using either electronic or steric "protection," one of the olefins of the conjugated diene was deactivated relative to the other for cross-metathesis. The reactions proceed with very high chemoselectivity and, when steric deactivation is used, very high diastereoselectivity.
- Funk, Timothy W.,Efskind, Jon,Grubbs, Robert H.
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p. 187 - 190
(2007/10/03)
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- Photochemical reactions of 1-acetyl-3-methylbicyclobutane
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The photochemistry of 1-acetyl-3-methylbicyclobutane in various solvents using λ 254 and 300 nm radiation has been studied.In inert solvents, photoisomerization occurs with formation of 3 and 4 with subsequent photoconversion of 3 into 5.The (3 + 5)/4 ratios are significantly greater for λ 254 than for λ 300 nm radiation, illustrating direct reaction from the ??* excited state(s).Additional photoreduction to 6 was observed for λ 300 nm in hydrogen-donating solvents, especially in diisopropyl ether and toluene.In carbon tetrachloride, at λ 300 nm, mainly the HCl addition compound 10 is formed via ketone-photosensitized decomposition of CCl4.Similarly, with methanol, 2-propanol and water as solvent or addendum, the 1,3-addition products 7-9 are obtained.Under all of these conditions, no photoproducts containing the intact bicyclobutyl group were found, illustrating the high chemical reactivity of this severely strained group.Mechanisms for the formation of the photoisomerization, photoreduction and 1,3-dipolar addition products are proposed.
- Cerfontain, Hans,Geenevasen, Jan A. J.
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p. 386 - 394
(2007/10/02)
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- ACTION DES COMPOSES ORGANOMAGNESIENS SUR LES PYRONES-2 - VII ETUDE DE LA STABILITE RELATIVE DES HYDROXY-6 DYHIDRO-5,6 2H-PYRANNES ET DES CETOLS TAUTOMERES CORRESPONDANTS
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In the reaction between organomagnesium compounds and 2-pyrones, the relative stability of the 6-hydroxy 5,6 2H-pyrans and their tautomeric forms (ketols) has no influence on the reaction pathway.When ethylenic ketols are obtained, the corresponding tautomeric dihydropyranols are prepared in a selective way by reaction of nucleophilic reagents on the 3,6-dihydropyrones.In the other hand, the exclusive formation either of the dihydropyranols or of the unsatured ketols E, during these two reactions, shows up that here is no equilibrium between these two entities in the experimental conditions.
- Lhoste, P.,Moreau, M.,Dreux, J.
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p. 1551 - 1562
(2007/10/02)
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