- NbCl3-catalyzed [2+2+2] intermolecular cycloaddition of alkynes and alkenes to 1,3-cyclohexadiene derivatives
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NbCl3(DME)-catalyzed [2+2+2] intermolecular cycloaddition of alkynes and alkenes was successfully achieved to give 1,4,5-trisubstituted-1,3- cyclohexadiene derivatives in good yields. The Royal Society of Chemistry 2009.
- Obora, Yasushi,Takeshita, Keisuke,Ishii, Yasutaka
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experimental part
p. 428 - 431
(2009/06/28)
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- Photochemistry of 2,5-dialkyl-1,3,5-hexatrienes. The influence of the ground-state conformation, controlled through steric substituent effects
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The photochemical reactions of a number of 2,5-dialkyl-1,3,5-hexatrienes are described.Variations in the selectivity of the reactions are observed, which can be rationalized by considering differences in the composition of the equilibrium mixture of conformational isomers, brought about by steric substituent effects.This result is in agreement with the NEER principle.In addition, examples are given of changes in efficiency of light-induced isomerizations, which are not restricted by the NEER principle.A reaction mechanism, involving a biradical intermediate, is proposed, which accounts for the formation of all of the reaction products containing a three-membered ring.MO correlation diagrams show that the formation of the three-membered ring as a primary step must occur in a conrotatory fashion.
- Brouwer, A. M.,Bezemer, L.,Cornelisse, J.,Jacobs, H. J. C.
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p. 613 - 624
(2007/10/02)
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- WAVELENGTH EFFECT ON THE PHOTOCHEMICAL REACTIONS OF (Z)-2,5-DIMETHYL-1,3,5-HEXATRIENE: SELECTIVE EXCITATION OF ROTAMERS
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The UV absorption spectrum of Z-2,5-dimethyl-1,3,5-hexatriene 1 is typical of a cZt triene, but the long wavelength tail indicates the presence of the (minor) cZc rotamer.The sudden change in the photoreactivity of 1 around 290 nm is in agreement with selective excitation of these rotamers.No indication is obtained for an intrinsic excitation energy dependence of the photoreactivity of the individual rotamers.
- Brouwer, A. M.,Cornelisse, J.,Jacobs, H. J. C
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p. 435 - 438
(2007/10/02)
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- Dienes as Possible Intermediates in the Catalytic Hydrogenation of Aromatic Hydrocarbons. 1. Dienes Derived from 1,4-Di-tert-butylbenzene and a Rhodium Catalyst
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The evolution of the products upon hydrogenating three diene derivatives of 1,4-di-tert-butylbenzene (1) is compared with the formation of 1,4-di-tert-butylcyclohexene (2) and cis- and trans-1,4-di-tert-butylcyclohexane (3 and 4) from 1 on an alumina-supported rhodium catalyst to determine which diene (or dienes), upon adsorption on the catalyst, best represents the structure of the intermediate formed in the rate-determining surface reaction of 1.Of the dienes 1,4-di-tert-butyl-1,4-cyclohexadiene (6), 1,4-di-tert-butyl-1,3-cyclohexadiene (7), and 2,5-di-tert-butyl-1,3-cyclohexadiene (8), the last exhibits best the properties expected if it forms the same adsorbed intermediate as does 1 at the same hydrogen pressure.Unlike the arene, however, the dienes do not yield the cis-saturated isomer 3 as an initial product at low hydrogen pressures.Instead, cis-3,6-di-tert-butylcyclohexene (5) is formed along with ene 2 and arene 1; the dienes tend to exclude the cycloalkenes from the catalyst, their effectiveness increasing in the order 6 7 8.The result indicates that at low pressures little of arene 1 (less than 5percent) is transformed directly to cis-1,4-di-tert-butylcyclohexane (3); instead enes 2 and 5 are produced initially, and because the concentration of the intermediate adsorbed dienes remains low during the hydrogenation of the arene, cis ene 5 is rapidly converted to 3 in the presence of the arene.At high hydrogen pressures, the cis ane 3 is an initial hydrogenation product of the dienes as it is of 1.
- Outlaw, James F.,Cozort, James Ray,Garti, Nissim,Siegel, Samuel
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p. 4186 - 4190
(2007/10/02)
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