Ionic photodissociation of polyenes via a highly polarized singlet excited state

Reddy, A. Mahipal; Rao, V. Jayathirtha

doi:10.1021/jo00051a011

Cited by 22 publications

(9 citation statements)

References 1 publication

(1 reference statement)

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“…After stirring for 1 h at 25°C, the product was isolated by chromatography (support: silica gel; eluent: diethyl ether and hexanes in a 2:3 ratio) and distillation as a colorless liquid; bp 132Ϫ134°C/0.1 Torr (ref. : [37] bp 140Ϫ145°C/0.3 Torr); n 20 D ϭ 1.4756; yield 3.0 g (54%). NOESY [38] cross peaks between δ ϭ 4.31 and 1.86 and δ ϭ 6.04 and 5.63 corroborated the assigned (E,E) configuration.…”

Section: 33-trimethyl-2-[(1e3e)-3-methyl-13-pentadienyl]cyclohexmentioning

confidence: 99%

The Organoalkali Route to Vitamin A and β-Carotene

2001

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The reductive cleavage of methyl vinyl-β-ionyl ether (1) or the deprotonation of 3,2Ј,6Ј,6Ј-tetramethyl-5-(1-cyclohexenyl)-1,3-pentadiene (2) gives rise to an organometallic C 15 species that combines selectively with a variety of electrophiles at the terminal chain position. Its reaction with aldehydes, however, is less clean. In particular, (E)-β-formyl-2-butenyl acetate gives the expected adduct 7a and, after dehydration, vitamin A acetate only in poor yield. The same is true for the analogous reaction with 2,7-dimethyl-2,4,6-octa-3-Methoxy-3-methyl-1-(2,6,6-trimethyl-1-cyclohexenyl)-1,4-pentadiene (1), quantitatively obtained by the treatment of vinyl-β-ionol with sodium hydride and methyl iodide in tetrahydrofuran or with dimethyl sulfate in the presence of sodium hydroxide under phase-transfer conditions, is readily cleaved by lithium metal or sodium/potassium alloy. The resulting heptatrienyl-type organometallic C 15 entity [1Ϫ3] can be trapped by standard electrophiles to afford, for example, the hydrocarbon 3, the silane 4 or the alcohol 5. As we have found more recently, the same C 15 species can be generated conveniently by the deprotonation of 3-methyl-5-(2,6,6-trimethyl-1-cyclohexenyl)-1,3-pentadiene (2) with sec-butyllithium or the superbasic mixture of butyllithium and potassium tert-butoxide. The required triene is easily prepared by a Wittig olefination of (E)-2-methyl-4-(2,6,6-trimethyl-1-cyclohexenyl)-2-butenal, [4Ϫ5] the key building block in the Isler/Hoffmann-LaRoche syntheses of vitamin A [5Ϫ7] and β-carotene. [7Ϫ8] (E)-3-Formyl-2-butenyl acetate is, along with vinyl-β-ionol, the major component of the Pommer/BASF route [9Ϫ10] to vitamin A. When this aldehyde was allowed to react with the organometallic C 15 species, regardless of [a] 3903 triendial, which ultimately affords β-carotene. Vitamin A acetate can also be prepared, this time in moderate yield, by functionalization through consecutive deprotonation, borylation, oxidation and acetylation of a C 20 pentaene hydrocarbon having the required skeleton. Both the C 15 and the C 20 organometallic key intermediates adopt spontaneously a zigzag-like outstretched conformation which, upon electrophilic trapping, directly and exclusively leads to the all-(E) configuration.

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Section: 33-trimethyl-2-[(1e3e)-3-methyl-13-pentadienyl]cyclohexmentioning

confidence: 99%

The Organoalkali Route to Vitamin A and β-Carotene

2001

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“…Later, the molecule can isomerize to form cis-retinyl acetate isomers, or to form a carbocation with the concomitant release of the acetate anion. 31 By analogy, the thermal energy provided during the early stage of the TG experiment could be sufficient to break down the acetate group (first process), while, at higher temperatures where much more energy is available, the molecule backbone could be dismantled (second process).…”

Section: Tg-ftirmentioning

confidence: 99%

Hyphenation of proton transfer reaction mass spectrometry with thermal analysis for monitoring the thermal degradation of retinyl acetate

Peinado

Mason

Biasioli

et al. 2017

Rapid Comm Mass Spectrometry

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Rationale: The processing of retinyl acetate, a vitamin and biomarker, at high temperatures causes significant decomposition of the compound and thus loss of its activity. The rate of mass loss can be conveniently studied by thermogravimetry (TG). However, this technique generally fails to reveal which compounds have evolved from the compound. In this work we propose a new hyphenation approach to continuously monitor the thermal decomposition of retinyl acetate and follow the evolution of specific volatile organic compounds (VOCs).Methods: Thermal degradation of retinyl acetate was followed by TG coupled to a direct injection mass spectrometer based on proton transfer reaction mass spectrometry (PTR-MS) to follow continuously the thermal decomposition of retinyl acetate. The results were also compared with those obtained by a second evolved gas analysis system based on the coupling of TG with Conclusions:The proposed TG-PTR-MS technique shows a great potential for following in real time the thermal degradation of ingredients such as retinyl acetate and identifying compounds evolved at specific temperatures.

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“…3), which had been previously observed by Blatz and Pippert (29) following addition of retinyl acetate to strongly acidic solutions. Subsequent triplet energy transfer studies have conclusively established that the excited singlet state, rather than the triplet state, is the progenitor of the retinyl cation (30). The fate of the retinyl cation is largely determined by the solvent.…”

Section: Photophysics and Transient Intermediates Following Photoexcimentioning

confidence: 99%

“…In nonpolar solvents, recombination is favored, yielding the original or an isomerized retinol. In polar solvents, while isomerization is also observed, the loss of a proton can result in the formation of anhydroretinol or interaction with the solvent can result in solvolysis products (30) (Fig. 3).…”

Section: Photophysics and Transient Intermediates Following Photoexcimentioning

confidence: 99%

Photodecomposition of Vitamin A and Photobiological Implications for the Skin†

Xia

Yin

et al. 2007

Photochemistry and Photobiology

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Vitamin A (retinol), an essential human nutrient, plays an important role in cellular differentiation, regulation of epidermal cell growth and normal cell maintenance. In addition to these physiological roles, vitamin A has a rich photochemistry. Photoisomerization of vitamin A, involved in signal transduction for vision, has been extensively investigated. The biological effects of light-induced degradation of vitamin A and formation of reactive species are less understood and may be important for light-exposed tissues, such as the skin. Photochemical studies have demonstrated that excitation of retinol or its esters with UV light generates a number of reactive species including singlet oxygen and superoxide radical anion. These reactive oxygen species have been shown to damage a number of cellular targets, including lipids and DNA. Consistent with the potential for damaging DNA, retinyl palmitate has been shown to be photomutagenic in an in vitro test system. The results of mechanistic studies were consistent with mutagenesis through oxidative damage. Vitamin A in the skin resides in a complex environment that in many ways is very different from the chemical environment in solution and in in vitro test systems. Relevant clinical studies or studies in animal models are therefore needed to establish whether the pro-oxidant activity of photoexcited vitamin A is observed in vivo, and to assess the related risks.

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Ionic photodissociation of polyenes via a highly polarized singlet excited state

Cited by 22 publications

References 1 publication

The Organoalkali Route to Vitamin A and β-Carotene

The Organoalkali Route to Vitamin A and β-Carotene

Hyphenation of proton transfer reaction mass spectrometry with thermal analysis for monitoring the thermal degradation of retinyl acetate

Photodecomposition of Vitamin A and Photobiological Implications for the Skin†

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