24315-14-8Relevant academic research and scientific papers
Selective isomerization of retinal upon two-photon excitation
Sashima, Tokutake,Hashimoto, Hideki,Koshihara, Shin-ya
, p. 380 - 385 (2003)
The products of photo-isomerization when excited directly up to the two-photon-allowed 1Ag- excited state of alltrans and five cis isomers of retinal were determined. The composition of the isomers at the photo-stationary state was drastically changed as compared to one-photon excitation. The production of the 13-cis isomer was selectively increased, and the production of the dicis isomers was observed in the case of a direct excitation upon the 31Ag- state, although they were hard to be produced by one-photon excitation in n-hexane solution. These results clearly evidenced that there exist isomerization pathways via two-photon-allowed excited states.
Vinyltin acetals in terpenic and nor-terpenic synthesis
Launay, Valerie,Beaudet, Isabelle,Quintard, Jean-Paul
, p. 937 - 946 (2007/10/03)
Vinyltin acetals obtained by stannylmetallation of homopropargyl acetals with Bu3SnMgMe/CuCN (E configuration) or by titanation of the corresponding alkyltin acetals (Z configuration) have been proved to be efficient storable precursors for the stereoselective synthesis of terpenoids, under mild experimental conditions.Due to the presence of a nucleophilic centre (Csp2-Sn bond) and of a protected electrophilic centre, they are also useful intermediates for an iterative synthesis of retinal and nor-retinoids. - Keywords: vinyltin; acetal; vinyllithium; monoterpenoid; retinal; nor-retinoid
A new prenylation method using the lithium enolate of prenal. Reaction with polyunsaturated aldehydes. A short access to retinal
Duhamel, Lucette,Guillemont, Jerome,Poirier, Jean-Marie,Chabardes, Pierre
, p. 4499 - 4500 (2007/10/02)
The enolate of prenal 1 prepared from the corresponding silyl enol ether 2 or enol acetate 3 led to a γ-regiospecific reaction with polyunsaturated aldehydes 4 yielding dihydropyrans 5 leading after hydrolysis to polyenals 7. This process allows the introduction of the isoprenyl skeleton. A synthesis of retinal, from β-ionylidenacetaldehyde is reported.
Photoisomerization of Hindered Poly-cis Isomers of Retinal. Regioselectivity And One -Photon-Multiple-Bond Isomerization.
Ganapathy, Srinivasan,Liu, Robert S. H.
, p. 6957 - 6960 (2007/10/02)
Direct irradiation of five dicis (7,9, 7,11, 7,13, 9,11 and 9,13) and one tricis (7,9,11) isomers of retinal led to regioselective isomerization at the 13,14 bond as well as multiple-bond isomerization.
Sensitized photoisomerization of all-trans- and 11-cis-retinal
Jensen,Wilbrandt,Bensasson
, p. 7877 - 7888 (2007/10/02)
The photoisomerization of all-trans-retinal (all-trans) and 11-cis-retinal (11-cis) sensitized by a range of sensitizers (porphyrins, Zn-porphyrins, naphthacene and a Zn-phthalocyanine) with varying triplet energies above and below the vertical triplet energy of all-trans-retinal (E(T) = 149 kJ/mol) has been investigated by continuous illumination and HPLC analysis of the products. The composition of the photostationary states, the relative isomerization quantum yields of all-trans and 11-cis, and the primary product ratios are reported. One photon-one bond isomerizations are dominant. With Zn-TPP as sensitizer it is shown that 11-cis and possibly all-trans undergoes one photon-two bond isomerizations as well. The quantum yields of photoisomerization of 11-cis sensitized by biphenyl (E(T) = 275 kJ/mol) and anthracene (E(T) = 178 kJ/mol) were found to be identical. Absolute measurements allowed evaluation of the overall triplet isomerization quantum yield of 11-cis, Φ(iso)(T)(11-cis→) = 1.0 ± 0.2, from which the corresponding quantity for all-trans, Φ(iso)(T)(trans-→) = 0.15 ± 0.05, was obtained. The overall photoisomerization quantum yield of 11-cis with direct excitation at 254 nm was determined as Φ(iso)(d)(11-cis→) = 0.42 ± 0.05 assuming all-trans and 13-cis to be the primary products. Quenching rate constants of several of the sensitizer triplet states by retinal were measured by laser flash photolysis. Possible mechanisms that could account for the experimental results are discussed, and it is concluded that the photoisomerizations most likely involve the retinal triplet states as intermediates. Within this model the observed sensitizer triplet energy dependence of the primary product ratios suggests that the triplet states of the different retinal isomers are different mixtures of triplet excited species, and that the composition of these mixtures depends on the starting isomers as well as on the sensitizer triplet energy for energies below the vertical triplet energy of all-trans-retinal. In the light of a review of the existing literature on the direct and the sensitized photoisomerization of retinals these conclusions suggest substantial corrections to the accepted picture of retinal photochemistry.
Transient Phenomena in the Pulse Radiolysis of Retinyl Polyenes. 1. Radical Anions
Raghavan, N.V.,Das, P.K.,Bobrowski, K.
, p. 4569 - 4573 (2007/10/02)
The spectra and kinetics of formation and decay of radical anions of a number of retinyl polyenes have been studied in methanol and 2-propanol at room temperature, using pulse radiolysis and kinetic spectrophotometry.The bimolecular rate constants for the attachment of solvated electrons, e-MeOH, to the retinyl polyenes are in the diffusion-controlled limit (8.6 x 109-1.6 x 1010 M-1 s-1).The radical anions of retinol and retinol acetate have their spectral maxima at 370-390 nm, and undergo decay very slowly with second-order kinetics.On the other hand, the radical anions of retinal, retinal n-butylamine Schiff base, and retinoic acid/ester have spectral maxima at 430-510 nm, and decay by first-order kinetics in methanol with rate constants in the range 1 x 104-1 x 106 s-1.The decay rates of radical anions of retinal and retinoic acid/ester become considerably longer on going from methanol to less acidic alcohol, 2-propanol, suggesting that protonation by solvent is the major mode of their decay in protic media.In the case of retinal Schiff base, an additional slow process with bimolecular rate constant 9.0 x 107 M-1 s-1 im methanol is observed for the formation of radical anion and is ascribed to the electron-transfer reaction from the methanol radical, .CH2OH.
PHOTOISOMERIZATION OF THE C18 KETONE IN THE VITAMIN A SERIES. SOLVENT EFFECT ON PHOTOISOMERIZATION OF COMPOUNDS RELATED TO RETINAL
Ramamurthy, V.,Denny, M.,Liu, R. S. H.
, p. 2463 - 2466 (2007/10/02)
The directions of photoisomerization of polyenals and polyenones are believed to be controlled by the relative ordering of n,?* and ?,?* states.
